### DESCRIPTION

This is a wireless linear power supply using a 16 bit Microchip PIC uController.

### TECHNICAL DETAILS / COMPONENTS

This board can take up to 24 Volts input.

The output is scaled by R5 and R20

The voltage divider R9, and R10 are to scale the output which is routed to RA1 on the PIC24/dsPIC33.

I used the Allegro? ACS712 for current sensing. The output PIN 7 of the Allegro? ACS712 is routed back to PIN 3 if the PIC24/dsPIC33.

The 1N5333 was included to prevent the output from being driven below ground due to suden removal of the PWM output from the PIC24/dsPIC33 when the circuit is connected to an inductive load like a motor.

Q1 and Q2 were originally NPN transistors which I have since replaced with Faichild F12N10L N-Channel enhancement mode silicon MOSFETS. Some day I will change the symbol and not just the name.

The Gate of the 2N7000 MOSFET transistor is connected to PIN 14 of the PIC24/dsPIC33 and R13. PIN 14 of the PIC24/dsPIC33 is set as open drain and is the source of a 12 bit PWM output. Risistor R13 is used as a pull up on the gate of the 2N7000 Mosfet. Risistor R2 in conjunction with C1 form a low pass filter which is used to convert the PWM into a DC value porportional to the PWM output. The output of the low pass filter is then router to LM2904 Op-amp 1 which is used to buffer the DC voltage output. The second Op-amp of the LM2904 is used as a driver for the Fairchild F12N10L N-Channel MOSFETS. NOTE: the feedback to the LM2904 is through these MOSFETS as well as R5 and R20.

To set the desired output range the values of R5, and R20 must be calculated. I origianlly used an older revision of Op Amps for everyone by  Bruce Carter and Ron Mancini ISBN: 9780128116487 to help me in the calculation of R5 and R20. The calculation of Voutput at the Source's of the F12N10L transistors is

Vin(1+R5/R20).

The value Vin is 0 to 3.3 volts. R5 if the feedback resistor, and R20 is the gain resistor for scaling the 0 to 3.3 volt input to the desired output. R7, R9, and R10 as well as LED1 add to the load on the output and are not used in the scaling formula.

The relays used are to allow orientation of the output to be changed as well is completely disconnect the circuit output from the outside world. Both relays are driven by 2N7000 MOSFET transistors. It is possible to substitute 2N2222 Bipolar NPN transistors. The PIC24/dsPIC33 output pins can be configured for open drain in software also.

A 25C320 can be used of IC6. The purpose for the 25C320 SPI memory chips is to hold calibration data. For each step of the PWM output an actual voltage can be recored and stored in the 25C320. Once this step is done a lookup based on the desired voltage output can be used to select the correct value to be put into the PIC24/dsPIC33's special function register to generate the specific output.

The use of an XBee board is used so that controlling Raspberry PI software or PC software are never directly connected to the circuit. This allow the board to be run remotely.

### LEARN / TOPIC / BUILD INSTRUCTIONS

This is a design which was inspired by Dave Jones of the EEVBlog

https://www.youtube.com/watch?v=CIGjActDeoM