Version 1 fail

A project log for Discrete Binary to 7 Segment Display

Logic circuit to take a binary input and convert it to a 7 segment display

SpencerSpencer 01/09/2016 at 21:435 Comments

V1 was a fail for multiple reasons. For some reason I decided to try to do the project Manhattan style. With the amount of connections and wires I had problems with connections. In addition to that I used cheap Fets from ebay of dubious reliability. What ultimately killed it however was the discovery that my schematic had multiple fundamental flaws.

Reviewing the schematic

I think this problem arose when I tried to convert it to using a common anode display. I got confused during this process and never discovered my mistake in time.

V1 trying to display a 1


Spencer wrote 01/10/2016 at 19:22 point

I went though and hand checked the function of a few gates after it failed to work. Some of them seemed to not work not mater what but did after I swamped them with new ones. There were also one or two shorts from gate to source.

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Yann Guidon / YGDES wrote 01/11/2016 at 03:36 point

good resolutions for the next assemblies :

* test each part before soldering

* test the circuit while assembly progresses

at least this should reduce the failure spotting time.

Good luck :-)

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Spencer wrote 01/11/2016 at 23:46 point

Making a jig to test smd fets would be a hack in of it's self! It's also easier to avoid touching.. And for testing it while building.... I would need to go about building it differently. Due to it's nature there are a few gates that are very interconnected and shoot wires off off to later stages. I think constructing a circuit of this size in one go is okay. I don't want to go bigger however. Really need to get insulated tweezers probably.

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Cymeriandesigns wrote 01/12/2016 at 07:43 point

I bought an inexpensive (@$US20) tester from Aliexpress that automatically tests passive components and transistors. It can even determine ESR for capacitors and pinout and gain for transistors. I test all my discrete components now before using them. There are a number of sellers of these kinds of testers, including on eBay.

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Yann Guidon / YGDES wrote 01/10/2016 at 07:18 point

What were the "dubious reliability" symptoms ?

FETs are very sensitive and fail easily anyway.

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