Design and Technology
My Own Personal Yellow Brick Road
A Little Bit Extra…

Steve has been building this amazing electronics teaching aid for one of his projects this semester and today was his first complete test using all 5 panels together…

Each panel interacts with the next to produce a final outcome of a binary to decimal counter that counts from 0-9 then resets. You’ve got the 555 panel with adjustable components to produce the initial signal pulse, this then feeds into two NOT gates forming a buffer to boost the signal from the 555. It then hooks up to a ripple counter made up of d-type flip flops and on into the 4 outputs representing the binary count, using a 4028 chip this output is then decoded into a decimal count. It doesn’t stop there, using the AND gate panel you hook up a gate to two of the binary outputs to get it to reset after counting 9. Phew! It’s a really comprehensive look at digital electronics, you have to be able to understand the 555 timers states, what various logic gates do, how to wire up a ripple counter form flip flops and why the whole thing works the way it does.

I’d love to have had this at the start of this project, it puts everything I’ve been looking at into one package :)

There’s only one problem… It’s not working properly:

Being a fault finding master now I volunteeredto help him work out what was wrong with it. The next morning I set about trying to work out what had gone wrong (Steve had already worked it out but it’s a good test of my new found confidence with circuitry so he let me have a play) The problem was the binary to decimal counter was not working correctly, after checking out the leads connecting all the components up it’s definitely a problem in the binary to decimal panel…

Using the output from the monostable 555 I tested each of the binary outputs in turn to see what lit up. No wonder the count is mangled! the binary inputs to the 4028 chip are wired in the wrong order! Steve needed to fix his project then so I didn’t have time to carry the test through to see which input was lighting which output to correct it but with a little more time I wouldn’t have any issues completing the fix.

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