Tuesday, May 31, 2011

Changes in the hardware

I've been having a secret the last week...

I accidentally fried some components in the Wonderboard while testing it.
If it was due to the reversed polarity of the cabling and lack of protective diodes or simply to weak cables to run the current needed should be left unsaid.

It also turned out the MOSFET got so hot simply because they were not saturated fully fast enough since the Arduino "only" has +5VDC@0.04A. The specs are around +10-20VDC@0.08A to trigger it, I learned after reading the spec sheet a little more carefully. This created a slow accelerating "puuuuuull" instead of an instant "PULL!". Doh...

Anywho -
I decided against repairing the board and ordered myself a couple of power driver kit's and a relay board from Sparkfun along with a MP3 board so I can get started with the sounds. These are professionally designed and all I need to do is to solder 'em up.

The soldering of the power boards went quick and well and they seem to function properly. Hopefully they'll handle the current needed. This kind of put me at a crossroad, should I -

A) Use relays to drive the flipper coils with the buttons directly and the power boards for the rest.

The obvious benefit would be to keep the high power flipper coils separated from the relatively small circuit paths of the power boards.

The drawback would the staggering 15ms time it takes to trigger...
Also I need to get more relays.

B) Use the power driver boards for all solenoids (but probably only one high power coil per board), and the relay to enable/disable current to the boards.

The benefit would be cleaner cabling and faster triggering of the solenoids, which is crucial for the flippers.

The drawbacks are the relays themselves - I don't know if they can handle up to +48VDC@7.6A...

The main reason for my doubts are the lack of details around +48VDC usage. The specs only show an example for +28VDC@20A... I do know they work with +48 VDC (I had to test it...Curious George ) but I don't know how much current they can handle at that kind of voltage and for how long. I did test it briefly by triggering the slingshot solenoids and it worked as a charm!

As for the MP3 board...
...Sadly Sparkfun had a stock error on their site so it turned out they had to backorder it. But it's shipped now but has not yet arrived. Will let you know how it performs as soon as I get it!

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