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RCFS question

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Hello All,

Any suggestions welcome, I have built the failsafe as described by MR.RC-Cam and it works very well, however sometimes if the power is switched off, and then back on within a short period of time there is no response from the servo, nor is there any failsafe action.

if the power is left off for some time then on next power up it seems okay.

would thid be some charge left in the decouple cap preventing the pic from resetting or something?

also, how much trouble would it be to add a low voltage activation on this system, by way of a zener ref and some use of the spare logic gate?

thanks in advance for any help


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(1) I'm not really sure, but the problem is probably due to the bulk filtering caps inside the Rx and servos. There are a couple hundred uF's when you add them all up. When you turn off the battery, they will hold a charge for several seconds. This can cause an incomplete PIC microprocessor reset.

As a test, stick your voltmeter across the servo power pins and turn off power. I'll bet that there is a small voltage that hangs around for a few moments. Even a few hundred millivolts can create poor reset conditions.

(2) Yes, you can use some external logic and a voltage reference such as a zener to create a low battery failsafe. I had drawn this up a long time ago, but could not find the schematic. All I did was add a gate to the servo input signal so that its output went steady state when the voltage was too low. This would force the PIC into the failsafe state.

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