PIC 12F675 with adaptor

[Wiebe@CARYA]

Hi,

Perhaps this is obvious, but I'm used to making software, and don't know
enough about hardware to solve this...

I programmed a 12F675 to blink a LED. This runs ok on the picstart
programmer.

Next step was to build a board to run the project. I only connect Vdd, Vss
and the LED/Resistor to pin 1,8 and 3. This works with a lab power supply.
It works for voltages from aprox. 4 to 8 volt.

But when I try a 6V net adaptor it doesn't work. It looks to me like the pic
resets continuously. The adaptor isn't broken (the led always burns). It
looks to me the voltage isn't stable enough. I put a 10nF capacitor over Vdd
and Vss, without success (also tried 4.7uF). I also connected MCLR (pin 4)
to Vdd (directly and with a resistor). Again without success.

Is there any way to get this working (preferably without a voltage regulator
like a 7805)?

Thanks,

Wiebe.

 

[Alan Holt]

The 12F675 is spec'd out at 5.5VDC max. Try using one of the newer LDO
regulators, and if size is a problem use one of the TO-92 regulators which
will handle up to 100ma. At least use a 5.1VDC zener diode.

 

[Wiebe@CARYA]

What do you mean by "net adapter"?

I think it's called a "wall mount"... Anyway, thanks for the reply. A diode
in serie with the power supply did the trick.

 

[Wiebe@CARYA]

Yeh, if its an adaptor you just plug into the wall, the voltage is probably
not regulated, some of those may not even have filter caps inside so you'll
get a 120 hz pulse even though it's DC out. you can try putting a diode in
series with the + out of the adaptor and the anode of the diode and a
capacitor on the cathode end and that goes to the PIC. I think the spec for
the chip is 4.5 to 5.5 volts and the diode should bring the 6 volts to 5.3
volts.

Thanks, that did it! I actually used a led in serie with the power supply
(didn't have a normal diode at hand). As a bonus I see the current demand as
light intensity. It will probably burn out when the current get's too
much...

Stange though, as I recall the thing did work with a lab power supply, even
at >6 V... Perhaps I'm mistaken...

And I probably get 100 hz pulses (European standard is 50 hz)...

Regards,

Wiebe.

 

[Wiebe@CARYA]

The 12F675 is spec'd out at 5.5VDC max. Try using one of the newer LDO
regulators, and if size is a problem use one of the TO-92 regulators which
will handle up to 100ma. At least use a 5.1VDC zener diode.

Not the size, but the distribution is a problem. To order it, I have to pay
delivery costs (EU 5,-) unless the order is EU 25,- or more.

I'll include some voltage regulators with my next order.

Thanks,

Wiebe.