Sunday, January 25, 2015

@MAKE Electronics Experiment 18 - 7-segment displays, 4026 counters, 555 timers

Here's the latest, from +Make: Electronics. Experiment 18 uses 3 single digit 7-segment displays, 3 4026 decade counter chips (1 for each digit, chained together so they roll over), 3 555 timers to get the circuit to run by itself.

I did a video but it was too big for Blogger to handle. See it in this post on Google Plus.

After I did the video, I added another 555 (actually the other side of the 556), an LED, and some additional resistors and capacitors.  The book gives really clear directions, My only variations were using the 556 (because I thought that would be interesting), using 3 1-digit displays instead of a 3 (my 3s are not individually addressable--only 12 pins as opposed to the 28-pin version Charles used). Also, I turned on the decimal point between digits 2 and 3 just for grins.

This was fun.  I just got a bunch of 7-segment displays from ebay, and it's interesting to see how to control them through chips only--no programming,

On power up, the counter runs. You stop it and clear it, then hit the start switch, After a delay, the LED lights and the counter starts.  You the hit the stop switch to time your reflexes. I almost got there, but I had some sparks and some component is likely fried. Since I got it almost working, I'll move on.

The next exercise is using logic chips, and I really want to do that. I ordered a whole bunch of them from ebay, but not all have arrived yet, including one of the 2 chips I need for this experiment.

While I'm waiting, I think I'll get the 7-segment displays working with arduino. In addition to the 1-digit displays I have some 3- and 4-digit ones., That could be interesting.  Less clutter on the breadboard...kind of cheating, which is why I wanted to do it Charles' way first.

Update 01/26/2014:  it turns out that the only thing I fried was the LED.  I got it working again (there were a couple of loose connections, too).  I think I will go on and fuss with the capacitor values to see if I can get it to count close to real time by 1/100s of seconds. could be fun. That, and the Arduino thing.

Update 1/27/2014:  the closest I could get was replacing R8 (2K2Ohms) with a 10K potentiometer (actually a knob I took from a fried clock radio) and 22 microfarad capacitor for C2.  Spec for C2 was 68uF but all I had was a 47.  Charles said to use a .1uF (then on the next page he said 1, which I think is what he meant because he said a 10 was 10 times the value).  I tried several values from 1 to 100, and settled on 22 because that gave me the most responsiveness from the pot.

This whole thing was really interesting--using different chips in multiple configurations, playing wiht the speed of the timer displayed on the 7-segment devices, etc.