TPIC6C695 wiring problems

Hi all,

I’m trying to drive a TPIC6C6595 using an arduino. I believe the arduino side of things is working fine, but nothing seems to be getting shifted out of the shift register. I’ve attached my circuit (based on the TPIC6C595 data sheet).

Pins 3,4,5,6,11,12,13,14 go to an LED (negative lead), which then goes to Vcc via a 220 ohm resistor. For clarity I’ve only shown pin 14 doing this in the diagram.

For testing purposes I have LEDs between each of DATA IN, CLOCK and LATCH to ground, and my arduino looks to be sending the correct signals - I can see CLOCK and DATA pulsing as expected, then LATCH going high at the end. Trouble is, I don’t see anything at all on the output pins.

I’ve triple checked things like the polarity on these output LEDs (even tried wiring the LEDs to ground, even though this chip uses active low). Can anyone spot any mistakes in my layout?

Of course you won’t, its got open drain outputs.

Draw this part out please:

For testing purposes I have LEDs between each of DATA IN, CLOCK and LATCH to ground,

Or in other words you do have current limiting resistors in series with each LED don't you?

Anyway without anything pulling up the chips outputs they will sit at ground doing nothing.

The outputs are shown with current limit resistors and LEDs wired to +5.
I was more concerned that the LEDs were killing the control signals.

Open Drain outputs, and the OP says (and indicates) that the LEDs+diodes are between the outputs and +V. Seems right.
Got the Anodes and Cathodes right?
Hope this isn't that, "oops, there's a break between the rails of the breadboard power strips" thing.

CrossRoads:
I was more concerned that the LEDs were killing the control signals.

Yes, that could have been the case. I had LEDs going from each of those three pins straight to ground; can’t have been helping much (see attachment). I’ve removed those, but still no activity on the output pins.

Ahhh. Looks like the breadboard that I'm working on is flaky. A bit of prodding etc and it's now working temperamentally. Time to solder it all on to some stripboard, and I reckon that will solve things. I'm sure those LEDs on the input pins were part of the problem too, so cheers for pointing that out (and thanks to everyone else for reading/suggesting)

Cool. Please let us know how it worked out when done. I'm currently working a project with 27 TPIC6B595s across three boards, SPI data coming at 8 MHz from a seperate 1284 board and data daisy chained thru, and its working great.