To briefly explain what I am trying to do;
Use the Stamp and Board of Education to drive an RC car DC drive motor and steering servo. The project goal is to simply drive the vehicle (autonomously) straight 10', turn right 90 degrees, drive another 6', stop and launch three raquetballs towards some (bowling) pins.
I think it would be best if I did not drive the steering servo·directly from the BOE and keep·a separate supply for the servo,etc.·The DC drive motor is powered by the RC rechargeable battery pack (tested at 7.8V and 19.5A no load). We also decided to use a spring mechanism for each ball each having a "trigger" that would be controlled by the microcontroller. The people responsible for this part of the design thought that they would use a spring loaded plunger mechanism inside a tube that will launch the ball when ready. They intended the trigger that would release the plunger assembly to be a cotter pin that would be pulled out by a small electromagnet. I purchased a ULN2308A Darlington Array to take the signal out of the microcontroller and hoped to use it to control a relay that would activate the electromagnet that would pull the trigger.
We could not get the ULN2308A to work. We tried different power supplies for the chip and never got a current out of it when the input to the ULN from the Stamp I/O was high (we used four AA batteries and then tried a 9V). We tested the outputs of the ULN and thre was no (measureable) current. We were hoping to drive a relay with it. I heard that the ULN2308A safely isolates the microcontroller signal from possibly damaging current and EMF. Also, the small trigger electromagnets that were supposed to activated by the relays were not strong enough to pull the trigger pin. We never got the relay to work with the ULN2308A but tested the mall electomagnets directly with a supply.
I realize that this is not a robotics message board but you all seem to have a lot of well rounded experience using microcontroller for projects.
I need to power the microcontroller, a steering servo, drive motor (RC battery), ULN2308 chip, and some kind of trigger or ejection mechanism for the balls.·I would like to know the best way to power everything else so that the Stamp is used to accomplish this seemingly simple task. Is it possible to tap into the RC battery supply to power the servo, ULN chip, and trigger mechanisms? Should I try to power the servo again using a 9V battery (I do not believe there is enough amperage). I believe that I need to separate the microcontroller supply from the servo supply.
As if this post is not long enough (sorry all) ... if there are any suggestions from people for a mechanism that will either pull the trigger pin for the launch mechanism or a completely different approach, I would be grateful. I thought of replacing the spring/trigger mechanism with a plunger/electromagnet system similar to pinball machines. Or maybe some self-contained device that will allow you to compress its spring and apply a voltage to release it. I thought of using servos to pull the pins too but, no matter what is decided, there is still the power issues to address.
I am obviously not and electronics guru so please be gentle with your suggestions, if you have any.