Using output pin to power peripherals; Op-amp, voltage reference, voltage divider....

[munromh]

Working on a new project that I want to be very low power while off and powered up with an interrupt on change. I'm planning on having the micro (16LF1847) powered directly by batteries (3 to 3.6 volts) with no voltage regulation. The project will have an LCD (CFAX12864T-TFH), voltage reference for the ADC, voltage divider to monitor battery voltage, and an op-amp (MCP6034). I'm thinking of using an output pin on the micro to power all the peripherals during operation. The current draw would be well within specs but I'm curious if there's anything I'm missing that would be detrimental to the accuracy of the peripherals? Or, would I be better off switching power to the peripherals through a MOSFET from the battery? I want to keep the part count low if possible.

Thanks

[towlerg]

Did you come to any conclusion about this, I've often wondered (powering external devices from PIC gpio) but never seen anything definitive.

BTW the 1847 has several fixed voltage sources which you could use to measure battery Vdd, no need for divider or subsequent power drain.

George

[munromh]

Hey George,

Thanks for checking in. I'm still working on the project, it's going VERY slow due to availability of time, and haven't come to a conclusion yet. I'll be sure to check back in when I finish up.

Best regards,
Mark

[andybarrett1]

Interesting thread for me…

I have just completed a small project using a 16f818 with LCD, RTC, etc turned on and off from GIO Pins… So would be interested to see how others might do it. I just used a FET 2n7000 gate driven via a 1k Resistor.

Few issues with back feeds around the LCD but cured with a well placed diode !

Andy

[towlerg]

Any chance of a circuit diagram, for a hardware dunce.

George

[Acetronics2]

Why would problems occur, if you do not draw too much current ??? just check the voltage vs current datas ...

I often use output pins to power TL431s as voltage refs ... absolutely no difference from powering a simple LED ...

Alain

[andybarrett1]

Any chance of a circuit diagram, for a hardware dunce.

George

Will sort it later George.

[munromh]

I didn't think there would be any problems but I thought I'd ask to see if there was something I might be missing.

Thanks for the response.

[andybarrett1]

Any chance of a circuit diagram, for a hardware dunce.

George

Thought the request was familiar.....Only difference to the circuit in the pic is I now have a LS Diode in the line from the FET Drain to the LCD Supply. I discovered some back feed from the LCD. The diode blocked it !

http://www.picbasic.co.uk/forum/showthread.php?t=19351

Andy