Specific board/direct connection
Hi Robologist /Voodoobot
I have a “spider” board that I want to use. Basically, it holds the PIC, crystal & caps, power led & reset switches and leads all the ports out to individual pins, all nicely ordered. Even has inline programming connections. (not too sure how to add attachments yet so look at the schematic here and layout here) Note: the layout shows screw terminal connectors and not pins but they are interchangable.
Its definitely not the smallest option but that is ok. This is not meant to be an exercise in miniaturization.
The nice thing is that you simply plug the sensor boards, h-bridge driver boards or anything else needed to interface to the PIC using leads.
I have also thought of modifying the layout so that opto-isolators can be put between the PIC pins and the pins that you connect things to. Currently these are protected by 220 ohm resistors.
To convert a pin from “input” to “output”, you swing the opto-isolator thru 180 degrees. I saw that idea on a Vellerman serial breakout board (that I also blew up!!!)
The opto-isolators will make the board construction more complicated because there will have to be either a lot of cross-link wires soldered in or the board will have to be double sided.
Oh well, install the free Eagle 4.14 software (again).
For example, a USB plug (to take the AIRcable unit) would have 4 wires, V+, V- connected to the power bus on the spider board and T, RX going to 2 pins in whatever port I decide on and would be on its own board.
In fact, each sensor or driver will be on its own board. I think it will make recovery from “blue smoke” a whole bunch easier and the opto-isolators will make it a whole bunch less costly…
One question though, on the
schematic , it shows pins 25 and 26 as TX and RX (terminating in JP5). Are these the pins to connect to the AIRcable unit or will any pins do?
If you have to play around with individual bits of the byte received (or sent), things get complicated and the dog gets beaten into the ground instead of getting a pat on the head. ;>}. If pins 25/26 are the ones to use, that means that port c only has 6 “useable” pins. Oh well, we will have to work around that slight inconvenience.
I dare say that if more inputs/outputs are needed, we can always use multiplexing, I2C or similar but that is WAY WAY in the future.
The platform will use some 12v batteries out of a couple of UPS’s which got a “slight” lightning zap to the controler boards.
Drive motors will be hacked windscreen wiper motors. May be interesting to get the oscilation to become full rotary motion and isolating the -ve connections from the casing so that I can reverse them without a big flash. No really serious issues there.
I’m not sure whether to use wheels (go-kart or small atv - 6"/150mm dia) or tracks (have no idea where to even start looking for them
Ok, enough from me, supper is calling (or more importantly, the wife)
All the best
Aubrey