Mini controller project required?

Question

I am somewhat new to this type of control device and require your assistance as to how i should approach my project.

I require the ability to turn on/off six independent outputs that will later be configured to bias 6 basic common emitter transistors (2N2222).

The latter small relays (12VDC/1A) will control an audio path etc..

However, the controller will be required to remember its last state before being turned off, the latter will allow the controller once turned on to resort back to its last state.

Example: The 6 relays (outputs) during the time the conrtoller is ON may be in different positions (open ~ closed), once the controller is turned OFF and then back ON it is important that the latter control states are re-initiated prior to when the controller was turned off etc...

*** This is not a homework project and i have no desire to use latching relays ***

Artwork concept:

http://i4.photobucket.com/albums/y109/emperor500/minicontrollerproject.jpg

Thank you

Answer 1

Assuming you can program a microcontroller chip...

Most microcontrollers have a low-power mode that puts them in a sleep state where they draw almost no current, but they retain their RAM contents etc. I would make use of that.

You could use a small backup battery that would keep the controller powered even if the 12V supply is removed. A 3V lithium coin cell will do. You just need to make sure that the controller monitors the main supply line so that it knows it has to shut down, otherwise it will just run down the coin cell pretty fast.

You need to check that the processor port outputs don't have internal pull-up resistors. If they do, then when the outputs are set low they will still be drawing current through these resistors; ideally you want the outputs to go high impedance in shut-down mode.

Most controllers can be woken up from a sleep state by a pulse on an interrupt pin. That could be from a simple pushbutton.

If you don't fancy building the whole thing from scratch, there are development kits for most of the common chip types. You can usually find one that has a board with the microcontroller plus some breadboarding space for other components.

I am using the C8051 series chips from Silicon Labs for my projects, they are really versatile. PIC chips are cheaper and more common.

Answer 2

See my answer under:

http://answers.yahoo.com/question/index;...

PIC has a nanowatt line which uses little power. Here's a selector:

http://www.microchipdirect.com/Chart.asp...

The 16F882 is a nice device. It has the self-write, lots of I/O, and is way overkill, but still only costs a buck. It runs from 2V to 5.5V, so you need regulator to run it off 12V. 3V lithium cell backup with germanium diode could keep memory. Run it at 32kHz to get probably about a 10uA draw. Use the watchdog timer to cut this to about 2uA. Also, can use self-write variant for permanent storage, possibly in lieu of backup battery. Also have LCD driver variants, perhaps they have higher voltage outputs that could reduce part count.

I would use n-channel FETS for the drivers, not the 2N222's. This allows the PIC output drivers to stay at legal voltages, because the gates are isolated. Make sure the voltage you run the PIC at turns on the FET adequately. I believe some are in the 2V range, many are within 5V.

U can use LED's instead of LCD. Use 1mA or 2mA diodes, big resistors to drop current low if less intensity acceptable. Put them in parallel with solenoids. Put the LED power supply thru a single additional FET if you want to be able to turn them off for power saving.