📬❄️📦Adafruit Holiday Shipping Deadlines 2019: Please place all UPS 3 Day orders by 11am ET Friday December 13 📬❄️📦
0

This is not not what I was expecting to find
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

This is not not what I was expecting to find

by Austringer on Wed Apr 14, 2010 12:54 pm

So I'm trying to reverse engineer something and came across something I've not seen, but I'm pretty much a beginner. A signal is fed into a tiny little circuit board composed of a regulated power supply and a single IC - a 7404 hex inverter. Tracing everything out, I found that what I have is an inputs that feeds into a not gate and the output from that feeds into the next not gate on the chip. It does this with two such signals. (The outputs go on to relays which ultimately turn on the coolant pump and the main motor on a CNC mill).

Until I saw this, I would have called a device that returns a 1 when given a 1 and a 0 for a 0 a wire. Is this just a matter of picking the right 7404 to turn a low quality signal into a nice clean signal, or is there something even more subtle that I'm missing?
Austringer
Austringer
 
Posts: 4
Joined: Wed Mar 05, 2008 12:55 am
Location: St. Louis

Re: This is not not what I was expecting to find

by zener on Wed Apr 14, 2010 1:20 pm

Well I suppose you could call it a poor-man's follower. It can take a high impedance signal and turn it into a somewhat lower impedance (although not that low). So maybe a poor-man's driver. There are lots of different ways to do things. In cheap products it is often surprising the cheap solutions designers find.

zener
 
Posts: 4487
Joined: Sat Feb 21, 2009 2:38 am

Re: This is not not what I was expecting to find

by uoip on Wed Apr 14, 2010 5:35 pm

Instead of calling it a wire, you can call it a buffer. It's explained here.

http://www.allaboutcircuits.com/vol_4/chpt_3/3.html


It can be done via a special buffer circuit, or by wiring two inverters together as you've described. The right choice depends on what parts are already available at what costs, or maybe whether other gates on the chip could be put to good use for something else.

Since you say the output drives relays, it makes sense that you might want a fairly robust signal for that purpose. The input is probably somewhat high impedance.
uoip
 
Posts: 127
Joined: Wed Sep 23, 2009 5:48 pm

Please be positive and constructive with your questions and comments.