ICL7107 not working on breadboard?

Question

I am building a very simple thermometer circuit on breadboard, based around the ICL7107. The 7-segment LED display I am using is made up of 3x TOD5261BE-N displays.

My intention was to make something nice and easy, just as an example circuit to show some kids at a local fair to try and get some interest in electronics. I have built circuits based on the ICL7107 and made a PCB for them and they work fine. Now I have built it on breadboard (I do not have time to design a PCB and order it/build it before the fair) and it will not illuminate the 7-segment LED displays.

The circuit is pretty much this:

The only difference is my input comes from the TMP35GT9Z which is similar to the LM35, and I am using a 0-5V supply. The V-, RefLo, InLo and Comm pins are tied to GND.

The oscillator pins are using a 100k resistor and a 10nF capacitor.

I have measured 100mV at he RefHi pin, and 212mV at InHi. Unfortunately, I do not have an oscilloscope at home so cannot measure the frequency of the oscillator pins.

Unfortunately, my laptop won't upload the pictures of my breadboard setup, or the pictures of me taking the measurements, so you'll have to take my word for the wiring being correct and the measurements accurate. I have double and triple checked the pinout and my wiring.

Is there some strange phenomena that means this IC won't work on breadboard or something? I have changed the oscillator components, tried a different IC and even tied the InHi to GND to try and force an output of all 0's but still the LED displays show nothing. If anyone can offer assistance, that would be great.

If pictures are needed, I can upload some tomorrow.

EDIT

Now able to upload pictures! First one is the breadboard set-up (I tried to keep it neat, so apologies for the mess of it! I'll tidy it up once its working!):

The next image is when I have turned it on (The last 2 digits are connected directly to GND via 470 Ohm resistors. This does 2 things. Firstly, proves the displays are working and secondly it shows it is a Thermometer as it will read °C:

With this, I find it strange that the -1 is being displayed, which are connected to pins 19 and 20.

These are pictures taken of measurements (directly on the IC pin). The first os of the reference (100mV) and the second is the actual input (212mV)

Just in case it was the clock line (as that is the only thing I cannot measure as I don't have a scope at home) I made a little 555 timer circuit and put it straight on pin 40 which I believe would be correct if you had an external clock. This still didn't do anything though.

_"Is there some strange phenomena that means this IC won't work on breadboard or something?"_ - if you are sure the circuit is correct then perhaps the problem is the _breadboard_! Check _every_ connection for continuity, even the ones you think must be OK. — Bruce Abbott, Oct 02 '19 at 00:19
Breadboards tend to be *very* unreliable. I once spent 6 hours trying to figured out why half of the channels on an I2C GPIO expander weren't working, only to discover that some of the IC pins had managed to wrap partially around the IC strip without touching the contacts. — Caleb Reister, Oct 02 '19 at 02:28
@BruceAbbott I did think it could be the breadboard. But I have checked for continuity, and took my measurements at the pins of the IC. If it were just a few pins, I would still expect at least some segments to light up when the output is set to 000 — MCG, Oct 02 '19 at 07:38
@CalebReister indeed, I have known breadboards to be unreliable also. But I took my measurements from the IC pins themselves, rather than somewhere else on the strip. It is also a brand new breadboard (I bought a few especially for this as I have a few other working circuits on them for demo) and the holes are still good tight fits — MCG, Oct 02 '19 at 07:40
@MCG That's actually the reason it took me so long to debug. Probing the pins directly applied enough pressure to cause them to make contact. When I probed it, everything appeared to be fine, but the circuit still wasn't working. — Caleb Reister, Oct 02 '19 at 17:59
@CalebReister Yeah, I understand that. The main issue is if it was a few loose connections, at least some segments should light up. If it is to do with the reference or input voltage, then it should just show an incorrect reading. It is a problem that none of them are lighting up at all — MCG, Oct 02 '19 at 22:51
I believe the full scale when using a 100 mV reference is 200 mV, so 212 mV is out-of-range. Could "-1" with all of the other digits blank be the over-range display reading? — John Birckhead, Oct 02 '19 at 23:02
@JohnBirckhead no, it should read 1999 if it is over-ranging. You are correct that the full scale is 200mV. I have over-ranged it and grounded the input to try and get it to display either 1999 or 000 but so far have not had it giving any output — MCG, Oct 03 '19 at 07:54
What do you measure at the output to the displays? Since this is non-multiplexed I'd expect static levels. — the busybee, Oct 08 '19 at 11:41
Including POL and AB3? Then these should not be lit. Another idea to check the clock: Feed the clock into a CMOS or TTL counter with enough stages as a divider. The last stage can be measured with an LED or multimeter at a slow frequency. — the busybee, Oct 08 '19 at 13:45
@thebusybee ahh, apologies, POL and AB3 are 0V, hence these are illuminated. As mentioned in the question, I omitted the 555 timer circuit and V- is just GND — MCG, Oct 08 '19 at 13:48
@MCG ideally, you'd post a schematic of what you have exactly, it's hard to even look at a breadboard, let alone try and figure out the changes of your circuit vs the other schematic. — Voltage Spike, Oct 08 '19 at 17:48
@VoltageSpike noted, I was trying to save time, but I'll draw up a schematic and post it tomorrow — MCG, Oct 08 '19 at 22:17
@VoltageSpike schematic updated to reflect mine. I'll draw my actual one tonight, but that is pretty much it — MCG, Oct 09 '19 at 07:29
I read the words "not", "working" and "breadboard", then I nodded in agreement. In my experience, some 95% of all breadboard problems are caused by the breadboard. A solder iron and some experiment boards will make lots of problems go away and it gives you some valuable experience soldering at the same time. — Lundin, Oct 09 '19 at 13:49
Oh, and always use a current limited power supply when tinkering with things like these! Otherwise when feeding directly from the battery, you'll risk frying stuff. — Lundin, Oct 09 '19 at 13:53
@Lundin I too have had bad breadboard experiences. This is why I bought brand new ones specifically for this. As it is for some example things to try and get youngsters interested in electronics at a local fair, I wanted to be able to take it apart after and re-use the components for something else. Hence breadboarding. I'm 99% sure this specific issue isn't the breadboard, or I am certain at least a few segments will be illuminated. I would solder it on protoboard if I had a mind to keep it after, as I don't need any practise with soldering, I've done more than enough over the years! — MCG, Oct 09 '19 at 13:53
@Lundin ahh, you can't see it, but underneath that tape where the power is coming in, I have hidden a small 5V regulator PCB on a bit of protoboard so I can power 5V circuits with a battery without having to bring out my power supply. So it isn't direct from the battery. It is 0-5V supply. I see I hadn't mentioned that anywhere, but it was stated the supply is 0-5V — MCG, Oct 09 '19 at 13:55
@MCG Okay, I got the impression you _were_ the student :) Though I'm pretty sure breadboards is a good way to scare away interested youngsters from electronics. As for re-using components, thr resistors are cheap and DIP sockets exist. Regarding the power supply, I'm sure you have a 5V regulator as in the schematic - that wasn't my point. Rather that it won't save the circuit from frying up. Old linear regulators like 7905 only have overheat protect, they cut supply when they get too hot by overcurrent. Too late at that point. — Lundin, Oct 09 '19 at 14:02
@Lundin nah, it's been a long time since I was a student. Breadboards are a good way to get quick circuits together and show what *can* be done. For some reason, anythign with visible displays and LEDs seems to be the most attractive to get peoples interests! I know the components are cheap, but I like building things when I feel like it, and not waiting for delivery. I used a regulator with a current limit built in, can't recall the exact one (was from work) but I made sure of that! — MCG, Oct 09 '19 at 14:19
verify all jumper connections , watch out for shorts on brown jumpers. Add ecap across V+, 0V rail ( eg >=10uF low ESR) — Tony Stewart EE75, Oct 12 '19 at 17:51
@SunnyskyguyEE75 all connections have been checked, double checked and triple checked. Voltage levels are correct, and no shorts found. I have tried different caps on the power rails, that doesn't make a difference at all — MCG, Oct 12 '19 at 23:26
@SillyInventor unfortunately not. I stripped down and rebuilt the entire thing and it did work eventually, but I am still unsure as to what exactly it was — MCG, Jun 29 '20 at 07:33

Phil G · Answer 1 · 2019-10-09T13:20:13.913

1

I can't tell for certain, but it looks like you have IN-HI connected to the +5V line (red wire) which matches up to the schematic, and the COMM pin (32) is going to the ground side of the supply. The COMM on these chips floats below the positive supply, and tying it down to the negative side will put the amplifier out of its common mode range. What that will do to the reading obtained isn't clear.

The GND pin of the 7107 also isn't supposed to be connected to the ground side of the supply - the 7107 is supposed to have a split supply, but you can use a single supply if you generate the ground level with a regulator - I'm guessing that's what you're doing there, since the charge pump approach in the schematic isn't on the board. Then you can connect the 9V between V+ and V- directly, and use the +5V regulator to feed the GND pin.

I fount this one here

What does happen when these go over-range is also not spelled out well, but there's a line in the datasheet -

This is because over-range is a low dissipation mode, with the three least significant digits blanked.

page 7 of the datasheet

so that may be why you are seeing what you do on the display.

There's a test function built in - pull the TEST pin high and all the segments will light up. First I'd suggest that you get the supply sorted out so that the input isn't out of its common range.

edited Oct 09 '19 at 13:20

answered Oct 08 '19 at 23:30

Phil G

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Thank you for the answer. The IN-HI pin is definitely connected to the output of my temperature sensor, which is where the 212mV was read. Unfortunately, I only have a breadboard wire kit, which has pre-cut wires so I wasn't able to colour co-ordinate as well as I would have liked. I'll be getting some wire soon though! It has been a while since I have done breadboard stuff! You are correct that I have COMM tied to GND, along with the GND pin, REF-LO, and IN-LO. I can't make out what is on the V- pin.... I'll check when I am home from work. I'll check the TEST function too. – MCG Oct 09 '19 at 07:15
+1 for the answer so far, I will need to check a few things though. I thought a 0-5V should work fine though. Your datasheet is a bit easier to read than the one I used, which was from maxim, and has a bit more information, so I think I'll follow that one now! Interesting about the over-range thing.... I have updated the schematic in the question to clear up confusion. Found one online that is pretty much exactly the same one I came up with – MCG Oct 09 '19 at 07:30
[Microchip's datasheet](http://ww1.microchip.com/downloads/en/DeviceDoc/21455d.pdf) says that TEST works only on 7106. – the busybee Oct 09 '19 at 11:29
@thebusybee damn, ow many datasheets are there for this? Lol. I can only assume there isn't much difference between the TC7107 and the ICL7107. A quick read through both datasheets looks pretty much the same – MCG Oct 09 '19 at 12:30
It's a well-copied product. I'm amazed that you can still buy a device that I used to build a multimeter around in 1984. Still works, though. – Phil G Oct 09 '19 at 13:05
@thebusybee I think that is just that the warning about the sustained DC voltage applied to the display is potentially damaging applies to the 7106. The pin description table doesn't differentiate the description of pin 37 for the two devices, as it does with pin 20. – Phil G Oct 09 '19 at 13:18
Well, I misinterpreted the block diagrams of the 7106 and the 7107. Sorry for the noise. – the busybee Oct 09 '19 at 14:15
@PhilG I have done a few things with this IC, it's a great little thing. Just frustrating I cannot get it working here. To confirm though, V-, GND, REF-LO and IN-LO are all tied to GND, with 5V being the positive supply. – MCG Oct 10 '19 at 07:45
No - GND and V- need to be separate, otherwise the analog section has no negative supply, and is trying to run at the negative rail. Datasheet gives - • COMMON MODE INPUT VOLTAGE (V- + 1V) < VlN < (V+ - 0.5V). In the schematic I included, the regulator holds V- at -5V relative to GND (the 7106 does this internally with a Zener), so with a 9V supply, V+ will be ~4V relative to GND. There was a charge pump in the first schematic you posted (as per p10 in the datasheet) that was meant to generate the negative supply. Everything else can be tied to ground. – Phil G Oct 10 '19 at 14:20
@PhilG ahhh, so I just need to generate a negative supply for V-? I think I may have a couple of ICL7660 ICs about somewhere. I'll put one of them on there to give me -5V for the V- pin. My damn simulation lied to me! Lol – MCG Oct 11 '19 at 07:17
If all the inputs meet spec and outputs are invalid, then fault – Tony Stewart EE75 Oct 13 '19 at 00:21
@SunnyskyguyEE75 that's not really very helpful is it? – MCG Oct 13 '19 at 18:39
If you have 0 and -5V then check POL signal on pin 19 – Tony Stewart EE75 Oct 14 '19 at 03:46
@SunnyskyguyEE75 You can see from the picture that the POL (minus) is low as the segment is lit – MCG Oct 14 '19 at 07:04

ICL7107 not working on breadboard?

1 Answers1