Electronics > Projects, Designs, and Technical Stuff

Show off your IC graves...

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david77:
I just had to fix my home made audio preamp, so I got this idea.
I thought it might be nice to show what kind of IC graves we used to build before the
widespread use of microcontrollers.

So, here goes one of mine. It is still in use everyday, it's the control logic of the preamp in my
Hifi system.
There are 5 buttons: Channel up/down, Tape 1, Tape 2, Mute. The logic turns relais on and off
according to wich button you press. The Tape 1, 2 and Mute function are simply some 74109 ff's
switching relais on and off.
The channel up/down buttons increase or decrease a 74192 decimal up/down counter. This puts out
BCD code (4 wires) wich shows the select channel on a nixie tube and triggers the input relais. The BCD
code is decoded with 7445 BCD-to-decimal decoders. There's some more stuff around the 74192 to limit
the count to 1...8.
On the back there's a tacked on board containing the "reset logic", this puts everything into a defined
state at power-up.
It could be done with one single micro...but I used 19 TTL IC's. The whole thing draws something like 800mA @ 5V!
I have to say, though, I learned something designing this. Wouldn't do that again, probably :P




Anybody got any sins like this still lying around or even in use?

EDIT: Just for the record: This circuit hasn't failed. What had failed was the P87LPC764 micro that
is responsible for the IR remote control! That was a project pulished in ELEKTOR magazine.

Zero999:
Why didn't you integrate the functionality into the P87LPC764?

I nearly made a bathroom fan timer consisting of a quad NAND, a 555 timer and a counter but changed the design to an MCU when I got around to buying a programmer.

Simon:
yea what really kicked me into MCU's was that I wanted to do a voltage indicator for a car/bike and saw that I could make it fully customizable and more functional with an 8 pin micro versus a 14 pin quad opamp chip

Mechatrommer:
@david77: great project! nothing substitutes DIY. u are lucky you got the chance to learn and done it that most youngsters will miss these days (mcu), including me (but i'm not young anymore :P)

david77:
I didn't integrate that into the P87LPC764 at the time simply because I didn't know how.
I knew my basic logic circuits though. And I had a shitload of old 74xx components and wanted to
learn how to really use them. So I came up with this.

In the end it's much like writing a piece of software, only you have to find a solution in hardware.
I wouldn't do this now, though my knowledge of mcu's is still very much limited I'd use a mcu and learn
some more about them. For me learning by doing works best.

For something like a bathroom fan timer I'd still use the trusty old 555... Why not?

@shafri: I'm not that young anymore...29...quite old for some.

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