PIC Cards : Schematics and PCBs

Sometimes the PIC is a part of the schematic and thus of the Printed Circuit Board (PCB) but, in other projects, the PIC is wired on a "stand alone" development board connected to the controlled device by several lines.
Over the years I used 16F84, 16F628, 16F873/876, 18F252, 18F2525...  microcontrollers and developed several PCBs for these chips.
Some of you asked me for the schematics, so I present here these home made development boards.

1. A new prototyping card for 28 pins PIC : 16F873, 16F876, 18F252, 18F2525, 18F2620, etc.( January 2011 )

• Many PICs have Analog to Digital converters inside the chip but most are missing any Digital to Analog function. This new card was designed to fix this drawback and includes a Microchip MCP4822 dual channel 12 bits D/A connected to the PIC via SPI lines. Output low-pass filtering is provided on the card.

• If not used, the D/A converter can be unselected through jumpers.

• The DAC MCP4822 data sheet is available here (Microchip Web site).

• RS232 MAX232A interface : this function can be selected or not via jumpers.

• PIC ports A, B and C I/O pins are available for connection to the external world via 5.08 mm terminal blocks on the edges of the card.

• ICSP connector for easy programing with Microchip ICD/PICKit3 interface or compatible programmers.

• Crystal, ceramic resonator or RC oscillator can be used for clock generation.

• Power supply : PCB footprints provided for either TO220 (7805) or TO252 SMD (LM1117) voltage regulators. Caution : solder only one of the 2 regulators on your PCB, according to the selected package !

• Foolproof power supply diode (Schottky or regular).

• A LED can be connected to RA5 via a jumper (useful when debugging). 

• Size : 86 x 74 mm (3.4 x  2.9"). 4 mounting holes in the corners.

Here are some pictures of the card, the first one with a 7805 voltage regulator, the 2nd and 3rd using a LM1117 SMD regulator located on the solder side .

       Card with a 7805 regulator on the components side                             Card with a LM1117 SMD regulator on the solder side (lower right corner)

Click on the picture to enlarge the schematic.

Note : the above PCB has been made by FAR CIRCUITS.

- The User Manual  is available : Click here to download this 500 kbytes PDF file

Software : a demo "LED18F2525.hex" program blinking the onboard LED and "SPI_ramp4822.hex" generating sawtooth  signals on the D/A converter output pins are available. These programs are designed for use with a PIC 18F2525 running at 20 MHz.

Click here to download these 2 hex files.

A picture of the dual ramp signals is shown below.

 

Note : I can provide interested readers with the C source code of these programs. However,  they are written with the CCS compiler and I can't say anything about their compatibility with other compilers. 

2. A simple 1-side development PCB for 28 pins PIC : 16F873, 16F876, 18F252, 18F2525, 18F2620, etc.

This card is easier to build because it is a one-sided PCB, the ground plane being the upper side of the PCB. There are no provision for D/A converter or ICSP connection. 

A RS232 link is available thanks to the MAX232A interface, but may be omitted if not needed.
Many terminal posts are available to connect the A, B and C ports to the external world.
The card is powered by any DC voltage greater than 8 Volts, a 7805 regulator associated with a foolproof diode providing the needed 5 Volts power supply.

You may download the PCB artwork as well as the components layout 

Note : This circuit is built on a dual sided PCB, the upper (components) side remaining unetched while the lower (solder) side is etched using the above mentioned artwork : the upper side is thus the ground plane. As most of the components pins must be insulated from this ground plane, I use a large drill (6 mm or more) to remove copper around holes not connected to ground. The photo below is a close-up of two insulated holes (upper part of the picture) and a grounded hole (lower part).

3. Development PCB for 18 pins PIC : 16F628, 16F84, etc.

Click on the picture to enlarge.

Click here for the PCB and here for the layout.

4. RS232 interface board.

Some PIC designs don't need any RS232 interface but such a circuit  speeds up software development : the hex file program can be downloaded in a few seconds into the PIC while it is in its socket, you can print some intermediate results for easier debugging, etc.
I recently developed a simple RS232 board fulfilling this job : it's merely a MAX232A connected to the RX and TX pins of the PIC on one side and to the RS232 lines on the other side.
In order to keep the PCB small, the 0.1 uF capacitors are SMDs.
Housed in a small box (see picture) this little gizmo is very convenient when it comes to debug a program.

The schematic (do you really need one) is shown below (click on the picture to enlarge)
.

Two PCBs were designed : the first one includes a 9-point D-Sub connector  while the second one, smaller than the first, don't have any RS232 connector, just some terminal posts.
Click here for the PCB artwork and layout of the design with a connector

and here for the PCB and layout of the no-connector design.
 

5. Downloads.

5.1 PIC80 Prototyping card.

- Schematic diagram
- PCB Artwork
- Components layout
- Technical User Manual (500kB PDF file)
- Demo hex programs


5.2 Simple one side PIC card

- Schematic diagram
- PCB Artwork
- Components layout

5.3 18 pins PIC card.

- Schematic diagram
- PCB Artwork
- Components layout

5.4 RS232 Interface board

- PCB and Layout of the card with connector
- PCB and Layout of the no connector version

Some other boards are in progress : please stay tuned !

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