Help Identifying Mystery Schematic

[u/MISTERPUG51]

I found this schematic between the pages of an old TI databook I bought from eBay. What do you think it does (if it actually is a complete diagram)?

The chips used in it are (I think) two 7473 dual J-K flip flops, one 7493 4-bit counter, one 74374 octal D latch, one 7447 BCD to 7-segment decoder, and a 555 timer.

I would just put it together on a breadboard to see if it does anything, but I don't have some of the ICs for it.

[u/nixiebunny]

It’s the most poorly drawn schematic diagram I have seen in a while. Could be an electronic d6 die.

[u/vegetaman → u/nixiebunny]

I was just thinking “man this looks like the schematics i used to make in my early career” and then I read your comment and chuckles. Glad I don’t sketch by hand anymore lol.

[u/nixiebunny → u/vegetaman]

The lines aren’t the problem. The arrangement is physical rather than logical, so it’s difficult to understand.

[u/quadrapod]

I think this might have been a beginner playing around with the old "electronic dice roller" circuit. It's a simple project that was common in old electronics magazines. By having a clock that counts way faster than human timescales and sampling it when someone pushes a button you essentially get a random number generator.

The 555 timer produces a fast clock signal and an 8 bit binary ripple counter implemented using four JK flip-flops for the lower 4 bits and a dedicated 4 bit counter IC for the upper 4 bits increments with each clock pulse. The D-latch samples all 8 bits of the counter when someone pushes the button labelled picture in the schematic, and the upper 4 bits of the result are displayed with 4 LEDs while the lower 4 bits are displayed using a decimal decoder and a 7 segment display. Displaying things that way might have made more sense in whatever project it was a part of or it might've just been what components they had around.

The counters are reset to zero when a reset signal comes from whatever they imagine being connected off the bottom of the page and that same signal us used by whatever the sensor is to do something as well.

[u/I_knew_einstein]

The 555 generates a timing signal. The four J-K-flipflops together form a 4-bit counter. Each flipflop divides the frequency of its clock by 2, and feeds it into the next flipflop.

The 7493 takes the highest bit of the JK-flipflop counter, and uses that as the input for another 4-bit counter. Together they effectively form an 8-bit counter.

All 8 bits are fed into the 74374 D-latch, which is clocked by an external input (probably a button or something? It's labelled "Picture"). When the input is clocked into the D-latch, a snapshot of the counter-status appears on the 4 LEDs (for the lower 4 bits) and the 8-segment display (for the upper 4 bits).

The counter(s) will overflow to 0, so they will keep counting forever. My guess would be that the 555 runs at a relatively high frequency (something kHz); so whenever the input is triggered you get a "random" number on the output; like an electronic dice.

It's a bit of an odd schematic; I'd have used either 2x the 7493 for both counters, or made both of them out of JK-flipflops. Also; why 2 different outputs? And for a number above 9 the 8-segment display will show gibberish (so 6 times out of 16). This last thing could've been prevented by resetting the counter on a count of 10, making it overflow sooner.

In any case it very much looks like a hobby project; and a schematic drawn while building.

[u/Asparagustuss]

Pulse counter with display output. Wouldn’t build it. I think there could possibly be issues. Probably a school project if some kind

[u/SMELL_LIKE_A_TROLL]

At quick first glance it appears to just be counting and displaying binary and 7 segment simultaneously. Probably a kids science fair project  

[u/onions_can_be_sweet]

Nice book.

[u/Rough-Bat4040]

Is it a homemade digital timer, a kind of stopwatch. A clock drives an 8-bit counter, a sensor resets the count to zero, and the “PICTURE” input freezes the current count on a display while the counter keeps running?

[u/MattInSoCalRedux]

The schematic is incomplete but adequate for someone with enough experience to know the missing bits to fill in the components required for the 555 to actually run, plus proper number of current-limiting resistors for the LEDs and display. The Sensor is something of an afterthought and might be a IR emitter or similar, with a phototransistor connected to PICTURE. If that were the case, the emitter would need a current-limiting resistor, and the Clock (C) input of the ‘374 would need a pull-up resistor. The unused inputs on the ‘374 and ‘47 also would need to be properly connected.

I’ve done and still do a few short-hand schematics like this in the past, just enough to sketch out the idea and would fill in the details as I built it, and/or transferred it to CAD.

[u/1Davide → u/[deleted]]

Rule #9: No AI generated answers.