gunrunnerjohn posted:I'm not convinced that you really need four one-shots. Why not a comparator ladder with four levels? An LED will be visible with a very short pulse, so the one-shot may just be icing on the cake to make it even more visible. I'd consider 3V, 6V, 9V, and 12V. Something cheap like the LM3900 and a resistor divider ladder driving an LED on each output.
You're basically describing making a low res flash ADC which is actually what I thought about too before going with the one shot.
It can be made to work but there's a lot of problems to struggle through. The trickiest part is the comparator itself because it's level sensitive, not edge sensitive, meaning if the input keeps changing, the output of the comparator immediately tries to respond to the change with its limited slew rate.
For example the LM3900 on page 3 is specified have a slew rate "SR" of 0.5V/us low to high output and 20V/us high to low.
The start of the DCS code is like 10111010... and each bit is like 0.3us long...
So the comparator will go up for 0.3 u-seconds at that slew rate and arrive at 0.5V x 0.3us = 0.165V. Then it will go down for 0.3us at 20V/us to about -6V. Then it will go up for 3x0.3us at the 0.5V/us rate to -6 + (0.3us X 3bits X 0.5V/us) = -5.55V. That means the set of 4 won't respond to the levels quite the way you think (it won't be like a comparator at DC). This is because the comparator slew rate can't keep up with the internal speed of the transitions inside the DCS packet.
This shows we need a comparator with slew rate that gets to the LED turn on voltage (or reliably exceeds threshold voltage of a following gate) within about half the bit time. (Roughly 3-4V/0.15us = 25V/us). Clearly this won't be a PDIP package, so it makes prototyping hard since you pretty-much need a custom PCB. Also you're on a battery so you want a single-supply comparator if possible.
I think you can figure it out, but it might take a bit of work to get it reliable.
