I think you may have the labels the wrong way around. TTL operates at 5 volts, with LOW (Logic 0) defined as 0V to 0.8V and HIGH (Logic 1) as 2.0V to 5.0V. Based on your video ( see 36:17 ), your device is in TTL mode when the switch is down. The other mode is CMOS, which typically works with 3.3V systems. In this case, LOW is < 1.0V and HIGH is > 2.3V. To test in CMOS mode, you’ll need to set your power supply to 3.3V and have the switch in the up position. More accurately CMOS (Logic 0) is 0V to approx 30% of VDD and HIGH (Logic 1) is approx 70% of VDD to 100% VDD. You can test a full range of CMOS modes such that a CMOS device designed for: + 3.3V operation will have: LOW: < 1.0V (~30% of 3.3V), HIGH: > 2.3V (~70% of 3.3V) + 5V operation will have: LOW: < 1.5V (~30% of 5V), HIGH: > 3.5V (~70% of 5V), + 1.8V operation will scale accordingly: LOW: < 0.54V (~30% of 1.8V), HIGH: > 1.26V (~70% of 1.8V) It may mean changing R1 (or inserting a pot) to allow you to work with the correct CMOS level.
As per the instructions of the original article, when you want to measure TTL you are supposed to connect the TTL clip to ground as well. In simulation I confirmed that this does indeed work. When the TTL clip is NOT connected the control pin is at 3.2V and when connected to ground the control pin is at 1.9V. So 0.1V under the threshold voltages. He measured the switch at 21:30. So I am assuming he oriented the switch in such a way that UP=Closed=TTL mode.
The TTL switch on pin 5 (control) needs to switch a voltage divider of two resistors, not just one. Put a pot between vcc and ground, with the center on pin 5 and you'll be able to dial in the exact voltage you want for TTL. But it will vary with the power supply voltage. Use a zener diode or 431 or just a red LED in parallel across the pot and you'll have a stable reference.
No need for a second resistor. This resistor works in conjunction with the internal threshold voltage level resistor divider ladder by lowering the upper threshold due to it being a shunt for the threshold ladder current to ground. The problem is that the oroginal design called for a BIPOLAR version of the 555, where the resistor ladder is based on three 5k resistors. He however used the CMOS version of the chip where the ladder is three 100k resistors instead. So he skewed the hell out of the divider network with his resistor.
I made one of these in electronics class in the '90's. The school ran out of 555's though so we were tasked with coming up with a different circuit. I somehow managed it with an XOR gate. I still have that probe somewhere. Good times.
Using the CMOS version ICL555/TLC555 instead of the Bipolar LM555/NE555 the circuit was intended for will make it necessary to recalculate the "TTL level threshold resistor" going to pin 5. This resistor is used to skew the internal 1/2 2/3 voltage divider ladder but was calculated for bipolar NE555 where the internal divider ladder consists of three resistors 5K each. On the CMOS versions the resistor ladder consists of three 100k resistors. So the unaltered "skew resistor" to pin 5 effectively gets the circuit stuck because it tampers with the threshold levels too much. Especially since you connected that resistor not to pin1 of the chip, but switched it to a point in front of the diode in the ground line, which is a more negative node (by 0,6V) compared to the ground of the IC at pin 1 that the chip's internal threshold ladder divider network is referenced to. Sorry, but if you deviate from circuit designs and use alternate chips you should study datasheets.
Had this in a previous reply you did but maybe more visible here. Sounds reasonable, though the values are not in the ILC555 datasheet I looked at. Presume you can just use an ohm meter between pin 5 and 8 to measure one of the 3 resistors and then pin 5 to pin 1 to measure the other 2 in series (and should be double the previous reading)?
Good call! There’s nothing regarding the internal resistors in the ILC555 datasheet, it just claims it should basically be a drop in replacement for the original NE555. I’m going to have to check.
@ Finally found my 555's and they are ICM7555IPAZ, apparently CMOS versions and pin 5 and 8 reads 5k and pins 5 and pin 1 read 10k. So it looks they are measurable and my ones are 5k resistors 👍
I have made a even simpler version with 2 LEDs and 2 resistors. I used an old syringe body as a "see-through" housing. For the prob tip I used to have a refillable printer ink cartridge kit and I use the needle out of it, soldered it right to the circuit board. Works great for what I needed it for.
@JanBeta sure, go for it. I only did it like that cuz that was what I had laying around. The syringe body was like 1 inch in diameter and where the plunger would come out the back side is where I ran into two wires for the positive and negative connections. You put the LEDs in series, you put your positive lead for the green LED and the negative to the red LED then the probe tip comes off the center between the two LEDS. Then just use resistors accordingly.
That circuit needs the OG NE555, not the CMOS variant you have. Probably the new part has different value resistors in the internal voltage divider than the BJT classic 3 x 5k ohms.
Happy New year 🎉 Jan and besides luck and good health I wish you that this year you treat yourself with some nice 3D printer so you can print something like custom cases and so on😊
Enjoyed the video, Jan, as I do all your videos. It was well done and I always appreciate seeing this kind of DIY design and assembly. As for the project itself, though, it's not a one I'd put the time and effort into. I have a logic probe. They're dirt cheap. If you can afford to eat at McDonalds, you can afford a logic probe. Mine never gets dug out of the drawer it's buried in. I just don't find it useful enough. It'll tell you "low" or "high" or "pulsing", but you can't see the voltage levels to see if things are floating and you can't see the frequency or duty cycle. When there are very basic oscilloscopes out there that you can buy for the price of two or three drinks at your local pub, I just don't see the value in a logic probe. That's just how I feel about logic probes, though. Still, I very much enjoyed the video. Sorry if I'm being too negative.
I built a logic probe that had a "floating" indicator. i cant remember where i got the circuit, but i know it's a single 74LS00 and a transistor. I'll have to reverse engineer it at some point
No worries! This was just a fun little project I’ve been wanting to build for a while and more about the journey than making the tool (although it‘s going to be handy to take "on the road" sometimes). :)
In a cozy little workshop, not far from here, Lived Jan the tinkerer, with gadgets quite dear. He loved to make circuits, with wires and glue, And one day he said, “I’ll make something new!” He found an old book from days long gone by, With pictures and diagrams-oh, my, oh, my! “A logic probe,” said Jan, with a gleam in his eye. “It tells you if circuits say ‘low’ or say ‘high.’” So Jan grabbed his parts: some wires, a chip, A breadboard, resistors-he was ready to flip! Two little LEDs, one green and one red, To show if a circuit was alive or instead… He soldered the pieces, one by one, Making sure every part was perfectly done. “The chip is the brain, the LEDs are the eyes, And the diodes will help make sure nothing fries!” When the circuit was finished, Jan gave it a try, He touched it to a chip-“Oh look, it’s high!” The green LED glowed with a soft, steady light, “It works!” Jan exclaimed, his smile big and bright. But then came the switch-a tiny, tough test, Would it handle both modes? Jan hoped for the best. He flipped it to “low,” but something went wrong, The probe stayed green-it was stubborn, headstrong. “Oh no,” Jan said, scratching his head, “This switch is stuck-it’s all high instead!” But Jan didn’t frown, he didn’t give up, He poured some more tea into his favorite cup. “Sometimes,” he said, “things don’t work right away, But tinkering teaches us more every day. The probe mostly works, it’s still good and strong, I’ll use it to fix circuits all day long!” And so the little logic probe found its place, Helping Jan with a smile on its bright, glowing face. It may not be perfect, but it was enough, Because learning and trying are the best kinds of stuff. So if you’re building something and it goes all askew, Remember the logic probe, and Jan’s lesson too: “Even if it’s tricky, don’t give up the fight, Because building and learning make everything bright!”
You might want to check if you have a short between pin 6 and 7. When I simulated the schematic it works perfectly. When I connected 6 and 7 though I get flashing leds, which in real world speed would be both on. In normal operation "red" needs to only be on... even when floating. Green ever only on when connected to high.
I built one of those around 1980. (I only knew ETI as a British magazine. Stareted buying them in 1977. Only later I realized it had Australian roots). Good tool, as long as you take into account that it can’t show (reliably) floating lines nor bus-contention, the same as most logic analyzers. Main problem is that you must take your eyes away from where you measure to look at the LED’s. With modern SMD I guess you can build it small enough to have the LED’s on the test-probe itself. A few years later, I built another version that uses an audio-tone to indicate lows and highs, as well as transitions. I preferred that model until eventually I could save enough to get an old Heathkit oscilloscope. Since then, I have never used a logic probe again. I came to prefer oscilloscopes, even for reading supply voltages, because at one glance you can see ripple, etc…. Nevertheless, I can remember my old logic probes fondly, and I did build and fix quite a few microprocessor circuits just using an analogue multimeter and my logic-probe. Nice and fun project to build and understand… next step is to build the logic-analyzer giving audio tones. Good 2025 to you, and I thoroughly enjoy your videos. 🎉🎉🎉👍👍👍
Nice project, could have used a socket with more 4 pins, and have the led(s) mounted there, solder the switch to the board + better cable management would then attach the board thru the switch to the case, use a single 3 legged dual color led, use a clear (covered) case no hole for led or replace with buzzer, is the heatsink/tab of the 7805 not ground ? hindsight is only useful when is someone else is trying it first, so thanks, diode 1 use a led to show circuit has power ?
The bipolar and CMOS versions of the 555 have different values for the internal resistors. That's your problem. Only the bipolar version actually has three 5Ks.
The D4 shifts the low level 0,7v higher for the 555. I would replace the D4 with a wire. I would check also the switch level with a second power supply if the TTL and CMOS levels are correct. At this state of the tester the fubction is not properly veryfied.
Isn't there a subtle difference between the NE555 and the ILC555? I don't recall but isn't there something about the trigger/threshold voltages that changes the way the output behaves? Easiest way ... just slap a genuine NE555 in there and see if the magic TTL mode switch works.
The internal threshold level divider is made from 5k resistors in the original bipolar LM555/NE555. But in the CMOS versions ICL/LMC555/7555 the correspinding divider is made from 100k resistors. The threshold levels stay the same but trying to skew the divider ladder with external resistances at pin 5 needs redesigning going from a bipolar to cmos 555.
In honor of this episode, I invite everyone to go and listen to Blue Öyster Cult's song _ETI._ A logic probe from a magazine abbreviated ETI is just too cool!
As someone who has never worked with 555 ICs, I would have loved a short explanation on how this circuit works. To me, the two diodes on the "probe" lead seem pretty useless as they basically conduct in just about any case (If D2 is conducting, D3 blocks, and vice-versa). I don't see why you can't just wire the probe signal to the two LEDs directly (maybe with a capacitor and/or transistor) to have one of them light up depending on the logic level? How does a timer chip come into play here?
The diodes on the probe are just there to "even out" the input voltage. They are only letting through their forward voltage. The 555 is basically used as a Schmitt-Trigger in this case (it has sooo many use cases), activating the LEDs. I recommend looking up the 555 pinout and finding out about the plethora of configurations and options it has to offer. It was a bit much to explain in a short video but of course I should at least have explained a bit more about this particular use case!
Dieses Gerät war zu Zeiten, wo Oszilloskope tausende von Mark gekostet haben, ein sehr nützliches Tool. Heutzutage hat ja so gut wie jeder Bastler irgendeine Art von Oszis, da sind solche "Logic Probes" ja schon fast verpönt, aber auf jeden Fall eine nette Bastelei ...😀
Isnt that resistor and cap acting like an RC filter, depending on the values its going to screen out a set of frequencies, maybe thats why it isnt working
I think the resistor is supposed to form a voltage divider together with the internal resistors in the 555 and thus change the threshold. But maybe I interpret that wrong.
It’s not going to work in CMOS mode as pin 5 is floating if the switch is open (C1 will block DC from getting to pin 5), and floating inputs to a CMOS IC isn’t good. I think this is why the original design called for a regular (TTL) NE555, as those can float high without problem.
The diodes are supposed to only respond if the voltage goes above its threshold. You want a gap to make sure it doesn't give a false response on spurious signals. Using a more sensitive diode actually defeats the purpose of a logic probe.
The two diode types should be similar enough according to the datasheets. If anything, the 1N914 have a slightly lower forward voltage but not by much (1V vs .7V). Should not really matter for this circuit. 🤔
Not sure. I think the resistor is supposed to act as a voltage divider together with the internal resistors in the 555 and thus change the threshold. Would probably not work on the VCC.
The positive voltage of the chip on pin8 is reduced by 0,6V due to D1 with respect to the +V clip. The ground of the IC is lifted by 0,6V due to D4 with respect to the ground clip. So the chip basically only operates within (+V - 0,6V) and (Ground +0,6V). If you are probing a digital waveform this signal may however swing between absolute +V and ground, which would be a swing greater than the voltage the chip operates at. D2 and D3 are there to drop the swing of a monitored waveform into the voltage range the chip works at by introducing the same drop that D1 and D4 introduce to the supply pins of the chip. This ensures that pins 6 and 2 are not driven more positive or negative than pins 1 and 8. Especially with the CMOS version of the 555 driving any input pin more positive than the positive supply of the chip (pin 8) or more negatove than ground (pin 1), may cause something called latch-up which may destroy the chip.
Yes, but in the Instructables it says to connect both the GND and TTL wires to circuit ground for TTL operation and otherwise just leave the TTL lead floating. That’s what my switch does, as far as I understand. 🤔
Looks like you used a 390 ohm resistor on the TTL line instead of a 3.9K resistor. It should be Orange-White-Red. Yours looks like Orange-White-Black to me. Unless I'm going color blind, the other two resistors also look wrong, the first band on all the resistors should be orange.
Resistors made from finest chinesium always need checking with an ohmmeter and then be put in a labelled bag. That aside; The issue with the TTL logic threshold switchover comes from a pit he dug himself.
@@JanBeta RED is logic High and Green is logic Low, thats the way it should be, you have it wrong in the video, thats what people see. swap the LEDs so its correct.
Also ich weiß ja nicht aber so auf den ersten Blick habe ich doch das Gefühl dass du über den einen Eingang über die D4 Diode messen willst und mit dem anderen Eingang über den R1 Widerstand. Also entweder oder aber dafür braucht man auch einen dreipoligen Schalter wo der mittlere Pin der Eingang ist der von außen kommt und der rechte und linke Pool entweder D4 verbindet ODER R1 verbindet. Oder versteh ich da was falsch? So verbindest du nur D4 und R1 miteinander oder mit der anderen Schalterstellung hast du nur R1 mit dem Eingang verbunden. Das geht so nicht. 😅 Oder soll das so sein?
Back in 2020 I bought 50x NE555 ICs, only needed one (was making a flasher relay, not for any purpose, just to pass the lockdown time!), but at £3.49 for 50x of them, it seemed more affordable than just a couple with a bunch of postage markup, and of course, 4.5 years later, can I find them? Can I heck!!! :P
Hi, here is something interesting to watch. Keep in mind that there are 5 movies in total, on this logic probe project. You can see that p5 in the title, it means part 5. ruclips.net/video/KDPp9r2tHYQ/видео.html I also dont think that pin5 of YOUR ILC555 CMOS timer, should be linked to anything else than a 100nF capacitor to ground. That capacitor is mounted there to stabilize the chip, to provide more stability in functioning. I sincerely never seen that pin linked to anything else.
I think you may have the labels the wrong way around. TTL operates at 5 volts, with LOW (Logic 0) defined as 0V to 0.8V and HIGH (Logic 1) as 2.0V to 5.0V. Based on your video ( see 36:17 ), your device is in TTL mode when the switch is down.
The other mode is CMOS, which typically works with 3.3V systems. In this case, LOW is < 1.0V and HIGH is > 2.3V. To test in CMOS mode, you’ll need to set your power supply to 3.3V and have the switch in the up position. More accurately CMOS (Logic 0) is 0V to approx 30% of VDD and HIGH (Logic 1) is approx 70% of VDD to 100% VDD.
You can test a full range of CMOS modes such that a CMOS device designed for:
+ 3.3V operation will have: LOW: < 1.0V (~30% of 3.3V), HIGH: > 2.3V (~70% of 3.3V)
+ 5V operation will have: LOW: < 1.5V (~30% of 5V), HIGH: > 3.5V (~70% of 5V),
+ 1.8V operation will scale accordingly: LOW: < 0.54V (~30% of 1.8V), HIGH: > 1.26V (~70% of 1.8V)
It may mean changing R1 (or inserting a pot) to allow you to work with the correct CMOS level.
As per the instructions of the original article, when you want to measure TTL you are supposed to connect the TTL clip to ground as well. In simulation I confirmed that this does indeed work. When the TTL clip is NOT connected the control pin is at 3.2V and when connected to ground the control pin is at 1.9V. So 0.1V under the threshold voltages. He measured the switch at 21:30. So I am assuming he oriented the switch in such a way that UP=Closed=TTL mode.
Yes, the wiring on the switch should be exactly as per the instructions. Up is closed=TTL, down is floating.
Happy New Years, Mr Beta. Love your videos. G'day from Australia.
Fun project!! Happy New Year from Canada
I might just try that its very simple, thanks for the inspiration to do so
Go for it! It’s super fun to build and actually a useful little tool. :)
Happy New Year!
I don't have a logic probe either, been meaning to make one, I have some 555s on my bench from another project, timely video! :)
Nice! Go for it. Really fun project (like many other 555 projects, of course)! :D
The TTL switch on pin 5 (control) needs to switch a voltage divider of two resistors, not just one. Put a pot between vcc and ground, with the center on pin 5 and you'll be able to dial in the exact voltage you want for TTL. But it will vary with the power supply voltage. Use a zener diode or 431 or just a red LED in parallel across the pot and you'll have a stable reference.
No need for a second resistor. This resistor works in conjunction with the internal threshold voltage level resistor divider ladder by lowering the upper threshold due to it being a shunt for the threshold ladder current to ground.
The problem is that the oroginal design called for a BIPOLAR version of the 555, where the resistor ladder is based on three 5k resistors. He however used the CMOS version of the chip where the ladder is three 100k resistors instead. So he skewed the hell out of the divider network with his resistor.
I made one of these in electronics class in the '90's. The school ran out of 555's though so we were tasked with coming up with a different circuit. I somehow managed it with an XOR gate. I still have that probe somewhere. Good times.
Nice! I guess there’s many ways to achieve similar logic probes with different components. What a cool way of learning electronics!
Happy new year! More 555 projects please!
Great 555 project! Happy New Year and best wishes in 2025.
Happy new year from Iceland! Been on my way to make a logic probe for a while now 😅 Thanks for fun videos!Keep them coming!
Great to see another video come out. Keep up the great work and wishing you and yours the very best in 2025.
Happy New Year, Here from the UK.
Frohes Neues!
Happy New Year Jan, and looking forward to many more videos in 2025.
Happy new year! Prosit Neujahr! :-)
Happy new year mr Jan!
Using the CMOS version ICL555/TLC555 instead of the Bipolar LM555/NE555 the circuit was intended for will make it necessary to recalculate the "TTL level threshold resistor" going to pin 5. This resistor is used to skew the internal 1/2 2/3 voltage divider ladder but was calculated for bipolar NE555 where the internal divider ladder consists of three resistors 5K each. On the CMOS versions the resistor ladder consists of three 100k resistors. So the unaltered "skew resistor" to pin 5 effectively gets the circuit stuck because it tampers with the threshold levels too much. Especially since you connected that resistor not to pin1 of the chip, but switched it to a point in front of the diode in the ground line, which is a more negative node (by 0,6V) compared to the ground of the IC at pin 1 that the chip's internal threshold ladder divider network is referenced to.
Sorry, but if you deviate from circuit designs and use alternate chips you should study datasheets.
Had this in a previous reply you did but maybe more visible here. Sounds reasonable, though the values are not in the ILC555 datasheet I looked at. Presume you can just use an ohm meter between pin 5 and 8 to measure one of the 3 resistors and then pin 5 to pin 1 to measure the other 2 in series (and should be double the previous reading)?
Good call! There’s nothing regarding the internal resistors in the ILC555 datasheet, it just claims it should basically be a drop in replacement for the original NE555. I’m going to have to check.
@ Finally found my 555's and they are ICM7555IPAZ, apparently CMOS versions and pin 5 and 8 reads 5k and pins 5 and pin 1 read 10k. So it looks they are measurable and my ones are 5k resistors 👍
Ive built this back in electronics classes. Almost 30 years ago. :-) wish I still had it.
You can build it again 🙂
@@rastislavzima More of an nostalgia thing. :) If i was to build one now it would not be like this. :)
Happy new year! I think I have 555 lying around so I will make it.
Always enjoy watching your videos 😊 Happy New Year 🎉
Happy New Year!
I have made a even simpler version with 2 LEDs and 2 resistors. I used an old syringe body as a "see-through" housing. For the prob tip I used to have a refillable printer ink cartridge kit and I use the needle out of it, soldered it right to the circuit board. Works great for what I needed it for.
Neat! Great idea to use a syringe and needle as the housing. I might nick that idea for a future logic probe if I may? :)
@JanBeta sure, go for it. I only did it like that cuz that was what I had laying around. The syringe body was like 1 inch in diameter and where the plunger would come out the back side is where I ran into two wires for the positive and negative connections. You put the LEDs in series, you put your positive lead for the green LED and the negative to the red LED then the probe tip comes off the center between the two LEDS. Then just use resistors accordingly.
Bring in the logic probe!
I can't believe I'm the first one to make this comment.
Better ask the MCP for permission first.
Happy New Year Jan! 🍻😊
That circuit needs the OG NE555, not the CMOS variant you have. Probably the new part has different value resistors in the internal voltage divider than the BJT classic 3 x 5k ohms.
Good call! Couldn’t find anything about the resistance in the datasheet but I’m going to have to check with a real NE555:
Happy New year 🎉 Jan and besides luck and good health I wish you that this year you treat yourself with some nice 3D printer so you can print something like custom cases and so on😊
Enjoyed the video, Jan, as I do all your videos. It was well done and I always appreciate seeing this kind of DIY design and assembly.
As for the project itself, though, it's not a one I'd put the time and effort into. I have a logic probe. They're dirt cheap. If you can afford to eat at McDonalds, you can afford a logic probe. Mine never gets dug out of the drawer it's buried in. I just don't find it useful enough. It'll tell you "low" or "high" or "pulsing", but you can't see the voltage levels to see if things are floating and you can't see the frequency or duty cycle. When there are very basic oscilloscopes out there that you can buy for the price of two or three drinks at your local pub, I just don't see the value in a logic probe.
That's just how I feel about logic probes, though. Still, I very much enjoyed the video. Sorry if I'm being too negative.
I built a logic probe that had a "floating" indicator. i cant remember where i got the circuit, but i know it's a single 74LS00 and a transistor. I'll have to reverse engineer it at some point
No worries! This was just a fun little project I’ve been wanting to build for a while and more about the journey than making the tool (although it‘s going to be handy to take "on the road" sometimes). :)
@@JanBeta That's a relief. I really hoped I hadn't offended you. Keep up the good work and Happy New Year!
happy new year Jan!
Happy New year Jan! 🎉😊
In a cozy little workshop, not far from here,
Lived Jan the tinkerer, with gadgets quite dear.
He loved to make circuits, with wires and glue,
And one day he said, “I’ll make something new!”
He found an old book from days long gone by,
With pictures and diagrams-oh, my, oh, my!
“A logic probe,” said Jan, with a gleam in his eye.
“It tells you if circuits say ‘low’ or say ‘high.’”
So Jan grabbed his parts: some wires, a chip,
A breadboard, resistors-he was ready to flip!
Two little LEDs, one green and one red,
To show if a circuit was alive or instead…
He soldered the pieces, one by one,
Making sure every part was perfectly done.
“The chip is the brain, the LEDs are the eyes,
And the diodes will help make sure nothing fries!”
When the circuit was finished, Jan gave it a try,
He touched it to a chip-“Oh look, it’s high!”
The green LED glowed with a soft, steady light,
“It works!” Jan exclaimed, his smile big and bright.
But then came the switch-a tiny, tough test,
Would it handle both modes? Jan hoped for the best.
He flipped it to “low,” but something went wrong,
The probe stayed green-it was stubborn, headstrong.
“Oh no,” Jan said, scratching his head,
“This switch is stuck-it’s all high instead!”
But Jan didn’t frown, he didn’t give up,
He poured some more tea into his favorite cup.
“Sometimes,” he said, “things don’t work right away,
But tinkering teaches us more every day.
The probe mostly works, it’s still good and strong,
I’ll use it to fix circuits all day long!”
And so the little logic probe found its place,
Helping Jan with a smile on its bright, glowing face.
It may not be perfect, but it was enough,
Because learning and trying are the best kinds of stuff.
So if you’re building something and it goes all askew,
Remember the logic probe, and Jan’s lesson too:
“Even if it’s tricky, don’t give up the fight,
Because building and learning make everything bright!”
Haha, thanks again! :D
I think you made the INTERNET.
The elders are waiting for its delivery...
Careful not to drop it
Happy new year from England Jan. The switch must bypass the ttl and push the circuit to ground giving you a constant high
You might want to check if you have a short between pin 6 and 7. When I simulated the schematic it works perfectly. When I connected 6 and 7 though I get flashing leds, which in real world speed would be both on. In normal operation "red" needs to only be on... even when floating. Green ever only on when connected to high.
I‘m going to check! That might explain it.
I built one of those around 1980. (I only knew ETI as a British magazine. Stareted buying them in 1977. Only later I realized it had Australian roots). Good tool, as long as you take into account that it can’t show (reliably) floating lines nor bus-contention, the same as most logic analyzers. Main problem is that you must take your eyes away from where you measure to look at the LED’s. With modern SMD I guess you can build it small enough to have the LED’s on the test-probe itself. A few years later, I built another version that uses an audio-tone to indicate lows and highs, as well as transitions. I preferred that model until eventually I could save enough to get an old Heathkit oscilloscope. Since then, I have never used a logic probe again. I came to prefer oscilloscopes, even for reading supply voltages, because at one glance you can see ripple, etc…. Nevertheless, I can remember my old logic probes fondly, and I did build and fix quite a few microprocessor circuits just using an analogue multimeter and my logic-probe. Nice and fun project to build and understand… next step is to build the logic-analyzer giving audio tones. Good 2025 to you, and I thoroughly enjoy your videos. 🎉🎉🎉👍👍👍
Nice project, could have used a socket with more 4 pins, and have the led(s) mounted there, solder the switch to the board + better cable management would then attach the board thru the switch to the case, use a single 3 legged dual color led, use a clear (covered) case no hole for led or replace with buzzer, is the heatsink/tab of the 7805 not ground ?
hindsight is only useful when is someone else is trying it first, so thanks, diode 1 use a led to show circuit has power ?
Great idea with the LEDs in the socket! Maybe it would even fit in a handheld probe enclosure that way. :)
The bipolar and CMOS versions of the 555 have different values for the internal resistors. That's your problem. Only the bipolar version actually has three 5Ks.
Good call! I’m going to check with a "real" NE555!
The D4 shifts the low level 0,7v higher for the 555. I would replace the D4 with a wire. I would check also the switch level with a second power supply if the TTL and CMOS levels are correct. At this state of the tester the fubction is not properly veryfied.
Isn't there a subtle difference between the NE555 and the ILC555? I don't recall but isn't there something about the trigger/threshold voltages that changes the way the output behaves? Easiest way ... just slap a genuine NE555 in there and see if the magic TTL mode switch works.
The internal threshold level divider is made from 5k resistors in the original bipolar LM555/NE555. But in the CMOS versions ICL/LMC555/7555 the correspinding divider is made from 100k resistors. The threshold levels stay the same but trying to skew the divider ladder with external resistances at pin 5 needs redesigning going from a bipolar to cmos 555.
@@randomsteve4288 Thanks. It's been ages since I even touched a 555 :)
Makes sense! I’m going to try with a real NE555.
In honor of this episode, I invite everyone to go and listen to Blue Öyster Cult's song _ETI._ A logic probe from a magazine abbreviated ETI is just too cool!
The ubiquitous 555, this is a task best suited to an LM393, but a bit of fun nonetheless.
Yup, there’s many ways to build logic probes with very few/common components. Maybe I’ll try another circuit sometime. :)
As someone who has never worked with 555 ICs, I would have loved a short explanation on how this circuit works. To me, the two diodes on the "probe" lead seem pretty useless as they basically conduct in just about any case (If D2 is conducting, D3 blocks, and vice-versa). I don't see why you can't just wire the probe signal to the two LEDs directly (maybe with a capacitor and/or transistor) to have one of them light up depending on the logic level? How does a timer chip come into play here?
The diodes on the probe are just there to "even out" the input voltage. They are only letting through their forward voltage. The 555 is basically used as a Schmitt-Trigger in this case (it has sooo many use cases), activating the LEDs. I recommend looking up the 555 pinout and finding out about the plethora of configurations and options it has to offer. It was a bit much to explain in a short video but of course I should at least have explained a bit more about this particular use case!
Dieses Gerät war zu Zeiten, wo Oszilloskope tausende von Mark gekostet haben, ein sehr nützliches Tool. Heutzutage hat ja so gut wie jeder
Bastler irgendeine Art von Oszis, da sind solche "Logic Probes" ja schon fast verpönt, aber auf jeden Fall eine nette Bastelei ...😀
Ja, ging mir auch eher um die Bastelei und vielleicht die Inspiration für Leute, die sich kein Oszi leisten wollen/können. :)
Isnt that resistor and cap acting like an RC filter, depending on the values its going to screen out a set of frequencies, maybe thats why it isnt working
I think the resistor is supposed to form a voltage divider together with the internal resistors in the 555 and thus change the threshold. But maybe I interpret that wrong.
It’s not going to work in CMOS mode as pin 5 is floating if the switch is open (C1 will block DC from getting to pin 5), and floating inputs to a CMOS IC isn’t good. I think this is why the original design called for a regular (TTL) NE555, as those can float high without problem.
The diodes are supposed to only respond if the voltage goes above its threshold. You want a gap to make sure it doesn't give a false response on spurious signals. Using a more sensitive diode actually defeats the purpose of a logic probe.
The two diode types should be similar enough according to the datasheets. If anything, the 1N914 have a slightly lower forward voltage but not by much (1V vs .7V). Should not really matter for this circuit. 🤔
Those diode marking are so tiny I sometimes install them backwards and might want to check the diode going to the switch.
I‘m going to double check but I’m pretty sure it’s the right way around!
G,day from Sydney Australia.
So the LED light on is the same as a signal on the oscilloscope probing a chip pin?〰️💡
Yes, the high LED indicates a high level that would also be visible on the scope (just in a lot more detail).
Could it be that the TTL side has to be bridged to high and not to low?
Not sure. I think the resistor is supposed to act as a voltage divider together with the internal resistors in the 555 and thus change the threshold. Would probably not work on the VCC.
Happy new year ! I really do not understand the D2 and D3. It seems to act as a piece of wire :/
The positive voltage of the chip on pin8 is reduced by 0,6V due to D1 with respect to the +V clip. The ground of the IC is lifted by 0,6V due to D4 with respect to the ground clip. So the chip basically only operates within (+V - 0,6V) and (Ground +0,6V).
If you are probing a digital waveform this signal may however swing between absolute +V and ground, which would be a swing greater than the voltage the chip operates at.
D2 and D3 are there to drop the swing of a monitored waveform into the voltage range the chip works at by introducing the same drop that D1 and D4 introduce to the supply pins of the chip. This ensures that pins 6 and 2 are not driven more positive or negative than pins 1 and 8. Especially with the CMOS version of the 555 driving any input pin more positive than the positive supply of the chip (pin 8) or more negatove than ground (pin 1), may cause something called latch-up which may destroy the chip.
Happy new year Jan, hope it will be better for you then last year! Seen the mail on Chat64? Let us know.
Sorry, I must have missed that email. I had a lot going on recently. :/ Would you mind re-sending? :)
@@JanBeta Done! :-)
The original circuit as printed in the magazine and shown at 2:16 wont ever work: Pins 1 and 5 are flipped.
Frohes neues Jahr. Bitte schalten die automatische Übersetzung aus. (Im creature studio) das hört sich sowas von grausam an... Danke;))
Ja, die ist wirklich schrecklich. Ich weiß aber nicht, ob ich die auf meiner Seite überhaupt komplett abschalten kann. 🤔
Guten Rutsch, Jan!
my EL-230 still runnig with his original 80's batteries!! :)
you need a switch, not an on/off. but one with 3 pins, and use the midle pin for the "power" 01---0p 02 - 01 to TTL, 0p topower and O2 to ground.
do you know what i meen?
Yes, but in the Instructables it says to connect both the GND and TTL wires to circuit ground for TTL operation and otherwise just leave the TTL lead floating. That’s what my switch does, as far as I understand. 🤔
@@JanBeta Hmm dosent make any sens
Looks like you used a 390 ohm resistor on the TTL line instead of a 3.9K resistor. It should be Orange-White-Red. Yours looks like Orange-White-Black to me.
Unless I'm going color blind, the other two resistors also look wrong, the first band on all the resistors should be orange.
Resistors made from finest chinesium always need checking with an ohmmeter and then be put in a labelled bag. That aside;
The issue with the TTL logic threshold switchover comes from a pit he dug himself.
I checked the resistor values, they should all be correct. That was my first idea, too. I’m going to double check.
LEDs, Green should be low and red should be high, that is the way it is on a purchased logic prob.
And that’s exactly what I did. It’s even in the thumbnail picture. ;)
@@JanBeta RED is logic High and Green is logic Low, thats the way it should be, you have it wrong in the video, thats what people see. swap the LEDs so its correct.
Oh, you are correct, sorry I misread. :D
Also ich weiß ja nicht aber so auf den ersten Blick habe ich doch das Gefühl dass du über den einen Eingang über die D4 Diode messen willst und mit dem anderen Eingang über den R1 Widerstand.
Also entweder oder aber dafür braucht man auch einen dreipoligen Schalter wo der mittlere Pin der Eingang ist der von außen kommt und der rechte und linke Pool entweder D4 verbindet ODER R1 verbindet.
Oder versteh ich da was falsch? So verbindest du nur D4 und R1 miteinander oder mit der anderen Schalterstellung hast du nur R1 mit dem Eingang verbunden. Das geht so nicht. 😅 Oder soll das so sein?
Happy New Year 🍀🍄🍻
It may be a mistake in the blueprint that needs to be worked out.
Logic probe: 555
Clock: 555
Nuclear plant: 555
ICBM: 555
FTL drive: 555
Quantum teleporter: 555
It’s the universal chip!
Back in 2020 I bought 50x NE555 ICs, only needed one (was making a flasher relay, not for any purpose, just to pass the lockdown time!), but at £3.49 for 50x of them, it seemed more affordable than just a couple with a bunch of postage markup, and of course, 4.5 years later, can I find them? Can I heck!!! :P
I can relate. 😅
Hi, here is something interesting to watch.
Keep in mind that there are 5 movies in total, on this logic probe project. You can see that p5 in the title, it means part 5.
ruclips.net/video/KDPp9r2tHYQ/видео.html
I also dont think that pin5 of YOUR ILC555 CMOS timer, should be linked to anything else than a 100nF capacitor to ground. That capacitor is mounted there to stabilize the chip, to provide more stability in functioning. I sincerely never seen that pin linked to anything else.
Watch out logic, you're gonna get a probing...
So even if this is the 3. version of the circuit, it still is a Beta version ☺
24:57 😂
Jan, I just noticed, why do you have a pride flag sticker in the lower-right corner of the TV monitor?
Because he's an awesome ally!
To show my support for the LGBTQIA+ folks. Some of whom I’m honored to call my friends.
I don't even have a hot glue gun. I really should quit the hobby and just sell off my stuff.
Hot glue is essential!!!
@@JanBeta amongst a few other things, like confidence.
Use wire wrap next time, lol.
Australia RuLz :)
Once again, not using your sponsor PCBWay for your project.
The enclosure is too big, and it's really a plus to use a double-sided PCB 😉
I think that too, is one or the other, no both at the same time.
I would have put the circuit inside a highlighter pen case with the probe stuck out the front.
The switch, should be 3 pin I'm sure
Happy New year Jan! 🎉
Happy New Year Umut! Long time no see! :)