[Opendispense] Latest additions

Harry McNally [email protected]
Sun Aug 3 10:59:33 2003


On Sat, 2 Aug 2003 22:19:38 +0800 [email protected] (Bernard Blackham) wrote:

> Hi all,

Hi Bernard

> What I'm still working on:
>  - decoding the serial protocol to talk to the coin mech

On that score, we could use two serial ports as listeners and
observe the traffic by clipping a little bit of electronics
on the board and dropping various coins through and also
make purchases that drop change. See how you go with it but
keep the hardware reverse engineering in mind as a backstop :)
 
> Can anybody think of any other hardware that we'll need/want to chat to
> that I've missed?

I've discovered some interesting things about the motor power supply.

There is a current limit circuit on the motor drive which
should start limiting at 600mA. When it does that, it will also
drive CPU pin PE0 (pin 17) from high to low.

Current limiting works by _lowering_ the voltage (if the motor shorts
out etc) so the current does not go beyond 600mA. 

What I can't work out (yet) is that there is another circuit that
uses an optoisolator (U24). This _appears_ to sense when the motor
voltage droops by extinguishing the opto led and allowing
PE1 (pin 18) to rise high.

So if you find anything sensing those two pins, it may be related
to motor overcurrent sensing. I am just puzzled why there are two
circuits sensing motor state in different ways.

Anyhoo, I'll have to get the circuit PDFs down into UCC at some point.
If I get the first (major) one done tonight, will Mailman spit if
I send as an attachment to the list ?

cu
Harry

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