Circuit for a 5V/3.3V PIC and a 3.3V Device plus Pickit3 programming.

Thread Starter

camerart

Joined Feb 25, 2013
1,914
Hi,

I want to control an SX1278 radio module with an 18LF2520 PIC with LCD, and program it with a Pickit3.

The SX1278 is a 3.3V MAX device and needs SPI to set it up, plus other connections.

The 18LF2520 will work on 3.3V or 5.V

The PICKIT3 uses 5V (5V suggested in the set-up) to program the PIC.

From tests, I've found that a 5V LCD will power from 5V and work with 3.3V DATA.

When wiring the circuit (using fuse wire) I connected the Pickit3 external power to the 3.3V. After programming the PIC runs if I use the external power from the Pickit3 circuit, but not when powering the circuit with it's 3.3V regulator.

I can't tell yet, but I will most likely have blown the radio circuit?

Can anyone tell me how I should have wired it up, to allow 5V programming, while not blowing the 3.3v units please?

Camerart
 

spinnaker

Joined Oct 29, 2009
7,835
The PicKit 3 will work at any voltage your chip is using. If you want the pickit to be the supply, it can be set to pretty much any level in the properties.

While the Pickkit maybe supplied by 5v from the USB it only applies the proper voltage levels to the chip.

Check your datasheet for the LCD. See if it will work with 3.3v. If not just order a 3.3v lcd.
 

Thread Starter

camerart

Joined Feb 25, 2013
1,914
The PicKit 3 will work at any voltage your chip is using. If you want the pickit to be the supply, it can be set to pretty much any level in the properties.

While the Pickkit maybe supplied by 5v from the USB it only applies the proper voltage levels to the chip.

Check your datasheet for the LCD. See if it will work with 3.3v. If not just order a 3.3v lcd.
Hi S,

I've ordered some 3.3v LCDs, but im mainly trying to get some results from the PIC and radio module.

I've programmed the PIC which only works when fed from the 5V Pickit3 external supply, but not when run on it's 3.3V regulator. This is the first puzzle. So far I have results on the LCD and flashing LED, but I may have 'popped' the radio module, after using 5V which was fed to the radio as well as the PIC.

C.
 

ErnieM

Joined Apr 24, 2011
8,029
Check of MCLR has a pull up. That's typically why PICs only run with the programmer connected.

The PICKit has a setting for the voltage it will supply. You need to set that.
 

Thread Starter

camerart

Joined Feb 25, 2013
1,914
Check of MCLR has a pull up. That's typically why PICs only run with the programmer connected.

The PICKit has a setting for the voltage it will supply. You need to set that.
Hi E,
Yes, the MCLR has a pull-up

Today I changed the MPLAB power settings to 3.375V, and powered the programming with the Pickit3. Then switched on the circuit (3.3V to PIC) no result. When powered by the Pickit3 external 5V circuit the PIC showed results. So the PIC can be programmed at 3.3V but it won't run until 5V is fed to it.

EDIT: I just checked the pull-up, and Ive connected it to the 3.3V positive, is this correct?

C.
 
Last edited:

Kjeldgaard

Joined Apr 7, 2016
398
It seems that there are a lot of Power Management and Brown Out settings on the 18LF2520.

And after a brief search, I found that there is a Brown-Out settings up to typically 4.3 and 4.6 Volt.

Can it be this setting?
 

Thread Starter

camerart

Joined Feb 25, 2013
1,914
It seems that there are a lot of Power Management and Brown Out settings on the 18LF2520.

And after a brief search, I found that there is a Brown-Out settings up to typically 4.3 and 4.6 Volt.

Can it be this setting?
Hi K,

Correct :)

My setting show BOR MIN or MAX, I switched to MIN and we have LED flashes and LCD results.

Well done!
Thanks to all.

C.
 
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