Hacking a treadmill. Need info on a shift register..

[eevfan007]

Hi!

I just bought a treadmill, and though I'd do some hacking. I have identified the main logic, and the keys (like speed, elevation etc) all goes into a shift register, that is then passed on to the main processor. My question is simple. I have not done any work with shift registers before, and this model uses the 74HC164N.

DATASHEET HERE: http://www.nxp.com/documents/data_sheet/74HC_HCT164.pdf

Am I correct in my assumption that this will send serial data to the main processor and back to the 74HC164? And am I further correct in my assumption that if I get in the middle of that I too can send serial command to the processor to control the treadmill ?

Some pictures:

The keypads (like speed up, down etc. Very simple pcb)


The shift register (with the connector from the first pcb with all the buttons). Shift register on the left.:


The main chip and EEPROM:



I can obviously solder directly onto the buttons, but I thought it might be possible to do all of this through serial. Can it?

[Rerouter]

Parrellel out serial in is for outputs not inputs,

it also ripples the outputs, which is a poor design move, (shifting in new bits changes the outputs)

Output the state you want, and then Clock high, this will shift the states across, so 0010000 becomes 1001000 (if asserting a 1)

[eevfan007]

Seems that I forgot to add the N at the end of the part number. If that's important. So: 74HC164N

[strangelovemd12]

The "N" just denotes the package, in this case DIP14.  If were in an SO14, for instance, it would be marked 74HC164D.

This stuff (how to string together the right part number) is in the "Ordering Information" section.  Some companies do a better job than others describing their coding system.