silly question; pickit2

[mab2]

Hi, hope this is a simple question but I can't find the answer:

I've got a project working using the pickit2 to supply the power to the circuit, but I now want to power the circuit from an independent 5v power supply. Should I disconnect the vdd line between the pickit and the circuit or leave it connected? or does it matter.

 

[ChrisP58]

You want to make sure that the setting in the PicKit programming application under the pulldown menu Tools/Target VDD Source is set to either > Auto-Detect or, to be sure, > Force Target.

 

[mab2]

Ah OK, and leave it connected I guess?

Thanks

 

[Vizier87]

Well I left mine connected to the power source and it can be programmed just the same. Unless you want to save battery power. May I know why do you need it to be so?

 

[mab2]

Well I left mine connected to the power source and it can be programmed just the same. Unless you want to save battery power. May I know why do you need it to be so?

when I started programming the pic there wasn't much hardware attached and I could power it off the USB ok, but now I'm using more power i don't want to overload the USB. The project will ultimately need it's own power supply anyway.

 

[Vizier87]

i don't want to overload the USB

Well if your supply is regulated I doubt it could "overload" the USB.

Cheers.

 

[ChrisP58]

We have on product in our shop where there is enough circuitry on the 5V bus such that the USB/Pickit can't power it all, so programming fails. Powering that product with it's normal operating source makes it programmable. The pickit is in Auto Detect mode, so it just announces that the target has it's own source, and turns off it's own power feed to the target.

The thing that you need to be careful of is to make sure that the target can run safely when powered up before the program is loaded. And, it you are using the icsp pins for I/O as well as programming, that whatever those pins do is happy being wiggled during program loading.

 

[mvs sarma]

too high electrolytic filter capacitor makes the pickit2 p\Vdd overloaded
even while external supply mode is used, we should not use th e internal osc mode in the micrcontroller concerned.
if normal crystal osc is used, one can use external Vdd

i case like yours,
better remove the electrolytic caps and then loads on the RB6 and RB7 pins
then connect to pickit2
it would programm
Later you can add them back in the target schematic

 

[mab2]

Thanks, I'm not using the 'pic' pins for anything ATM.

The caps are small and the reg is an LM317. I was thinking about running it at 5.12v or 4.096 to give a convenient mV/step on the A/D.

I am using the internal oscillator though - why can't I use the internal osc with ext vdd?

for info, it's an 18F4520 in case that makes a difference.

 

[ChrisP58]

During programming, the Pic uses the internal oscillator.

Whether or not you use an external oscillator for program execution is immaterial, provided that the pins needed for programming are not affected.

 

[mab2]

OK, Good.

Thx