Show off your IC graves... - Page 1
Forum section: electronics / projects

author: david77
author_rank: Frequent Contributor
timestamp: October 30, 2010, 01:04:50 am
content: 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 thewidespread use of microcontrollers.So, here goes one of mine. It is still in use everyday, it's the control logic of the preamp in myHifi system.There are 5 buttons: Channel up/down, Tape 1, Tape 2, Mute. The logic turns relais on and offaccording to wich button you press. The Tape 1, 2 and Mute function are simply some 74109 ff'sswitching relais on and off.The channel up/down buttons increase or decrease a 74192 decimal up/down counter. This puts outBCD code (4 wires) wich shows the select channel on a nixie tube and triggers the input relais. The BCDcode is decoded with 7445 BCD-to-decimal decoders. There's some more stuff around the 74192 to limitthe count to 1...8.On the back there's a tacked on board containing the "reset logic", this puts everything into a definedstate 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, probablyAnybody 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 thatis responsible for the IR remote control! That was a project pulished in ELEKTOR magazine.

author: Zero999
author_rank: Super Contributor
timestamp: October 30, 2010, 09:05:04 am
content: 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.

author: Simon
author_rank: Unknown
timestamp: October 30, 2010, 09:42:10 am
content: 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

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 30, 2010, 10:19:12 am
content: @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)

author: david77
author_rank: Frequent Contributor
timestamp: October 30, 2010, 04:23:39 pm
content: 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 tolearn 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 learnsome 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.

author: Zero999
author_rank: Super Contributor
timestamp: October 30, 2010, 05:02:30 pm
content: Software is free and easy to modify, hardware is harder and costly to change.I couldn't use the 555 timer alone because it was more complicated than a simple timer. I wanted the user to have a choice between the fan being on continuously and on for a certain period of time: pull the cord switch once and it'll be on for 10 minutes, pull again to turn it of or pull the cord twice to turn the fan on continuously and pull again to turn it off. This kind of behaviour is difficult to implement with a 555 timer and logic gates but trivial with a microcontroller.Here's a thread describing the circuit operation and the code.https://www.eevblog.com/forum/index.php?topic=1293.0

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 30, 2010, 05:14:53 pm
content: Quote from: david77 on October 30, 2010, 04:23:39 pmdont worry! life begin at 40, i still have 7 yrs to be there. i mean nowadays, everybody are looking torward mcu/digital design (including me), fewer and fewer will be interested in analog design, as quoted from other thread IIRC not sure where. i wish i was a EE graduate, but i'm still gratefull to be Mechy's.

author: jahonen
author_rank: Super Contributor
timestamp: October 30, 2010, 06:01:24 pm
content: Quote from: shafri on October 30, 2010, 05:14:53 pmI think that digital is just a wide-bandwidth nonlinear analog design. Analog and RF properties of digital signals is more important today than ever. Anybody who fails to recognize this will have trouble with Mr. Maxwell later on, when one tries to market the product and notices that EMI compliance or acceptable signal integrity is actually required. Pure digital thing exists only in daydreams of mathematician.Regards,Janne

author: Simon
author_rank: Unknown
timestamp: October 30, 2010, 06:40:16 pm
content: Quote from: jahonen on October 30, 2010, 06:01:24 pmVery true, I think many people like digital because it takes away a lot of things to worry about as it's on or off and to some extent that works particularly say when you want to have a predictable output and are using parts where no two are the same (any part), but you can't use this theoretical model right through as you need to also consider how things in the real world work.

author: Time
author_rank: Frequent Contributor
timestamp: October 31, 2010, 02:31:11 am
content: Analog is too intrinsic to the science behind electronics to be thought of as being something that could possibly be phased out.