Use 8M as a normally open gnd switch?

[dchurch]

I would like to use the 8M to supply a normally open momentary ground.

I need a one tenth second ground pulse output every 3 seconds, but without having this same output going high.

The brief load when low is less than 5mA.

I understand that a high, nap, low ... loop will control my transistor which in turn will supply my ground pulse, but_

I'd rather not waist the transistor and extra resistors if there's a command solution or better approach.

Is there another option, for example a pin condition set as open by waiting for input, or ..., that I'm overlooking?

The use is for a device that is constantly on but is only activated by momentary ground input (and high to this input would be bad).

Thank you,
dchurch56

 

[Tom2000]

Sure. Idle your pin as an input, set it to an output to send your ground pulse, then set it back to an input.

Tom

 

[Michael 2727]

Setting a pin as an input makes it high impedance, neither high or low.
On power up I think all the pins are set as inputs, may pay to bouble check though.
Just remember to set the pin as an input after the low period to make sure.

 

[hippy]

On an 08 or 08M, pins 1, 2 and 4 ( legs 6, 5 and 3 respectively ) can be used as inputs and as outputs in the manner described.

The only question is, exactly what are you pulling low ? That will dictate whether you need a transistor or it can be done by the PICAXE directly.

 

[dchurch]

Thanks,

You guys great. I thought that the input command might work for this but I din't want to spend time barking up the wrong tree. I'll set up a breadboard and run the tests.
I believe my short low pulse will be pulling less than 5mA so the 8M alone should be fine.

Regards,
dchurch56

 

[hax]

Ensure that it does not float higher than 5V or higher than your input voltage (whichever is lower). What are you switching?