I remember years ago seeing a clip that would fit over an IC and show the logic state of each pin on an LED (or an LED pair). Something like this
Do such clips still exist but with LEDs on top and what are they called?
-- James Harris
This is my take on such a device:
Another DIY design was published in the Aug. 1987 issue of the Australian version of "Electronics Today International", with the largely inaccurate name of "In-Circuit Digital IC Tester". Therefore I made it available on my webpage about DIY IC tester designs:
As noted in my description there, it powers the LEDs from the outputs of the chip that it's clipped to, which might cause issues in circuits that can't supply enough extra current.
Similar pre-built devices were sold at the same time, but I don't know of any still available.
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Do you mean something like this?
I think this was only for TTL levels and 5V power.
That brings back memories!
I wonder why they fell out of favour. Is there a better way to monitor digital ICs in-circuit these days?
-- James Harris
Yes, that's the kind of thing. I take it they are a bit passe these days. That one certainly looks ancient.
-- James Harris
I just gave away something like that to a young boy that was bread boarding some 7400 series logic circuits. Had it for years but hardly ever used it. I don't recall who made it,but it was in a box that had that clip on thing and 2 other logic probes. I think one gave out pulses and one would light up a led on a pulse. Seems they could be switched for either 5 volts and the one for cmos.
is
I remember seeing several variations of the IC Clip that had a housing on t op of the clip that contained some logic and LEDs over each pin. IIRC, Jam eco used to sell them and the one I had was made by SWTC (South West Techni cal Corp)IIRC - a kit mfg in the mid-70s. I never found it all that useful except to find stuck outputs. Was not ver y useful if the logic was driven by some trigger that you had to somehow se t up. ALso, catching a 1ms or less pulse with your eye is kinda tough. No clue if anything like that exists now. To trace out logic, I use my 16-digital channel MSO. There are 'logic boxe s' around that effectively are the 16 or 32 channel DI of a MSO. Cant reca ll their names ATM. Good luck J
Of course there are Logic Analysers, but they were around back then too. These days there are some cheap options for connecting to a PC though, eg.
The clip-on indicators were easier to use, but I think the key limitation is that the only signals that can be reliably analysed are those slow enough for the eye to observe changing state. That's why I wanted to build one that allowed various methods to be used in order to sample and effectively slow down the display.
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That's true. As just one example, I have a computer board with a
4-to-16-line decoder which I suspect of possibly asserting more than one output at a time or of not asserting some outputs at all. But without single stepping the CPU or running a small test program, which is not currently possible, I'm not going to see much from pin states which vary so quickly.I wasn't aware of logic analysers. They sound far better if they have enough channels. I see many with 8 or 16 channels but a more expensive Hantek LA5034 which apparently has 34 channels:
Whether such a piece of kit would be generally useful or not, such an analyser wouldn't help in this specific case as it could not be used to check the above decoder without also using a test program to cycle through the inputs. The decoder is not socketed so I guess all I can do is unsolder the chip and test the 16 permutations of its inputs on a breadboard. If I'm wrong and there is a better approach please say!
-- James Harris
I don't have any recommendations, but the specs for that model look like they should suit your application. Make sure that whichever device you buy supports all the logic signals (TTL/CMOS etc.) that you might want to use, at all the voltages that you might be running circuits at (the linked one should).
Well I just gave you a link to my page on IC testers, hint hint. Some support various approaches to in-circuit tests, but new testers are a bit thin on the ground.
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They aren't much use for anything faster than a burglar alarm. Usually they just told you high, low or 'pulsing'. Nobody builds burglar alarms out of TTL anymore.
Is there a better way to monitor
A logic analyzer. You can get slow USB ones for under $100, and pretty fast ones for $300.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net https://hobbs-eo.com
Just curious, can you supply a pointer or two to some of the high end analyizers at ~$300-400? Thanks J
A $300 analyzer is pretty far from "high-end". Have a look on Amazon--that's where I found them.
I've never actually needed a logic analyzer--the FPGA/CPLD tools and a scope have always been enough. (I'm not a big FPGA guy myself.)
Cheers
Phil Hobbs
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net https://hobbs-eo.com
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