Germain Morbe wrote:
>
> Hello,
>
> has anyone a LOW COST / LOW CURRENT idea that could help solving the
> following alimentation problem?
>
> A 16C505 or 12C508 shall be used as an ecoder for a 12V battery powered 3
> button handheld transmitter. Because of the needed code completion feature
> after button release, the power must be present permanently / resp. as long
> as the PIC needs it.
>
> The two approaches i see are:
>
> a) use a very low power 5V regulator which is comparable expensive.  That
> way the PIC could wakeup from sleep at button activation for as long time as
> needed to complete a message after release of the button.
>
> b) use a low cost 7805 regulator or a zener which draws to much current to
> be allways on. Thus, the buttons need to switch the power directly and the
> PIC needs to hold the power in the ON-state via some transistors. After
> completion it could cut itself and also the stabilizing circuit from power
> by releasing the transistors.
>
> Is there a third possibility i dont think of?  I feel that from the two
> mentioned either has its drawbacks in a low cost radio control? What would
> the gurus advice?
>
> Germain Morbe


I'm not a remote guru, but it does seem the max
priority is to conserve the battery.

I would use the buttons to switch the entire
power to the PIC (and regulator), and use a fet
or transistor to keep the power on under PIC
control until it decides it is finished doing
the task.

For the 3 button dilemma, I would use 3 diodes,
one from each button to the PIC power Vdd, this
is the common for all three buttons of course.
Then each button is also connected to one PIC
input pin. This will allow any button to power
the PIC, and also activate its own input pin.

The diodes will drop 0.6v, assuming cheap diodes,
but you only have to get the PIC running long
enough for it to turn the transistor on, and
then you have full power anyway. :o)
-Roman

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