these blinkin' inputs

trav · Posted: Sun May 12, 2013 12:33 pm Post subject: these blinkin' inputs

I've been playing around lately with chips like the 4512 and 4051. They are very useful for generating melodies: plug an oscillator source into some or all of the 8 inputs, then clock the A B C pins and listen to the common out. What would be useful is visual representation of which channel is selected at any given moment. Is there a way of wiring an LED to each of those 8 inputs so that it only lights when that input is selected?

I can see how to do it by using another 4051 to control the LEDs, but perhaps there is a way without spending a second chip.

JingleJoe · Posted: Sun May 12, 2013 1:22 pm Post subject:

noep, you'd have to introduce a voltage to the input to light the LED, which may bias or overpower your signal.
Why not put lights on the control inputs and learn to count in binary? Smile

I'm sure there is a binary to 7 segment display converter IC out there too.

trav · Posted: Sun May 12, 2013 1:39 pm Post subject:

> Why not put lights on the control inputs and learn to count in binary?

Oh, I've done that, and it's fine for simple things like straight counting to eight, but when A B and/or C are getting pseudo-random clocks, or even just when bit order is swapped, it starts to get hard to see what's going on.

I do like the 7-seg display idea! If it's going to take a second chip anyway I'll definitely do one like this

trav · Posted: Sun May 12, 2013 1:58 pm Post subject:

looks like I want a 4028 (BCD to decimal decoder) to light LEDs, or a 4511 (BCD to 7-segment decoder) to drive a 7-segment display

trav · Posted: Sat May 25, 2013 7:20 pm Post subject:

well, I tried both. I ended up using a 4543 to drive the 7-seg display, and it works well with the 4051. The 4028, on the other hand, is giving me some trouble. As you can see in the attached video, the 4512 is operating correctly, playing notes 1-8, but during the count I get more than one LED lighting. As I understand the 4028, only one output should be high at any given moment, so why this strange behaviour? Anything to do with sharing the ABC inputs between chips? Each input jack is wired to an LED indicator, to a pulldown resistor, and to the input pin on each chip. This works with the 4543/4051, why not with the 4028/4512?

4543_4028.wmv

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trav · Posted: Tue Jun 04, 2013 6:20 am Post subject:

The LEDs on the ABC inputs were drawing too much current. Rather than up the current-limiting resistor values or use transistors I decided to split and buffer the inputs. I rigged up a 4010 hex non-inverting buffer as a triple 1-in 2-out multiplexer. The jack goes into the buffer, then one out powers the indicator and the other out goes to the inputs of the other chips in the circuit.

I quite like this separation of visual and audio signals and may well order a batch of 4010s or 4050s to extend the idea across my lunetta.