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KF4SQB

Need help with LED display circuit

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Hi, everyone. I've been keeping an eye on the main board for a few years now, but just signed up for the forum. I'm now wishing I'd done this earlier! Anyway, here's my problem:

I'm trying to design and build a circuit to use a 5-bit binary input to drive a dual seven-segment LED display. I'm using a TO-220 package 7805 regulator for power, a 28F010 Flash EPROM for binary to BCD conversion (overkill, I know, but it's what I had laying around), and a pair of HD14511BP ICs to handle BCD input and display drive. My problem is that the 7805 gets way too hot, despite the fact that it's load is nowhere close to it's max output, and the display flashes "00" over and over, very fast, no matter what the binary input is (possibly a bad program in the PROM, as I'm no programmer ::) ). If anyone wants to see the program in the PROM, ask me and I'll email it to them, as I have no way to host it for download, or just write a new one and send me. I want the display to show "01" for binary "0", numerically sequential through "32" for binary "31". Here is the circuit (the pin numbers for the display module are incorrect in the schematic, but the "names" applied to the pins are correct):

binarydisplayis1.jpg

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Hi K,
The 7805 needs a heatsink for cooling. Its input voltage is very high and causes it to heat nearly 3 times as much as if it has an 8V input.

The inductor L2 destroys any high frequency voltage regulation for the ICs and should be removed. Then C3 and C4 will provide a low impedance supply voltage at high frequencies. Maybe that is why the display is wrong. Add a 0.1uF ceramic disc capacitor at the supply pins of each IC to make sure.

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