Board 3 - PIC 16F873A
Processor board 3 - PIC16F873A
Fig. 1 PIC 16F873A board
Description:
This is a processor board, and can take various 28 pins Microchip PIC processors. This one is fitted with a PIC 16F873A, but was also tested with a 16F876 and 18F2320.
The 16F873A has enough memory for small projects, hardware UART, I2C and SPI ports, 5 10bits ADC and 3 timers. It is plenty to test a lot of the PIC features.
Its main purpose is to be able to develop on the 16F type processor.
It runs at 16 MHz, has on board voltage regulator (5V), and has 3 8 bits interfaces, 1 I2C, 1 serial, and 1 ICSP connectors.
The board can be powered by an external 8V main power supply block, or PSU3 (8V from USB port).
Specifications:
ProcessorMicrochip PIC 16F873A
Interfaces3x8bits, 1xI2C, 1xRS232
Clock16 MHz quartz (20MHz max)
Power supply8 to 15V
Memory4 K word Flash for program
192 bytes RAM
128 bytes EEPROM
Timers3 (2x8bits and 1x16bits)
2 capture, compare and PWM modules
Analog to digital5x10bits channels
Programmingon board ICSP connector
Schematic:
The components used are mostly components I already have, or recycled from various hardware. Some values are not critical. It is mainly a power supply, and connecting the various interfaces connectors to the processor.
The power supply is filtered by C1 and regulated to 5V with U1. D1 rectifies the supply voltage if needed, and also protects the board if the power supply connection is inverted. The board can be powered by a small main 6 to 12V transformer. U1 might need to be fitted with a heat sink to prevent it from overheating. It can also be powered by the board PSU3, which supplies 8 V from a USB port.
The processor U2 gets its power from the on board regulator or the ICSP programmer. D2 (Schottky for low voltage drop) supplies the power from the regulator, D3 from the ICSP. C3 filters U2 power and needs to be fitted as close as possible to the chip.
The value of the quartz is fairly open, but must be 20MHz maximum. I had a spare 16MHz one. The processor will need to be configured for HS oscillator type. C5 and C6 can be between 15 and 33 pF.
C3, C4, C7 and C8 are filters capacitor. Their value is not critical, but 100 nF is a good one to use. You can use between 10nF and 1 uF.
The usual reset signal is provided with D4, D5, R1 and C9. The led simply shows when the board is powered on.
The 3 8 bits interfaces connect port A, B and C to an 8 bits type bus, common across the various boards. Port A only provides RA0 to RA5. Pins 6 and 7 are not connected.
Pins 6 and 7 from port B are isolated with a resistor (R2 and R3, 4.7k, but not critical) on the interface, so the various boards plugged in will not interfere with programming. (RB6 and RB7 are used on the ICSP connector to program the processor.
The RS232 (TTL level with Rx and Tx signals) and I2C interfaces just take their signals from the appropriate pins of the processor.
The interrupt signal from the I2C interface is connected to signal Int0 (RB0)
Fig. 2 Board 3 schematic
Construction:
The processor boards are build on prototyping strip boards. It can be a bit long, as they are many signals to route. Use the schematic and replicate it on the board. Use a socket for the processor U2.
K7 is for the RS232 interface. The signals are TTL level, and a converter can be fitted on it to provides proper RS232 signals. A pin from the header needs to be remove (pin 4)
Once all the components are soldered, you can test the board as described below before inserting the processor in its socket.
| Interfaces pinout | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Power supply | 8 Bits | I2C | RS232 | ICSP | |||||
| 1 | V+ | 1 | Vcc | 1 | Int | 1 | Gnd | 1 | nc (LVP) |
| 2 | Gnd | 2 | bit 7 | 2 | Vcc | 2 | Vcc | 2 | RB6 |
| 3 | bit 6 | 3 | Sda | 3 | Tx processor | 3 | RB7 | ||
| 4 | bit 5 | 4 | Scl | 4 | NC | 4 | Gnd | ||
| 5 | bit 4 | 5 | Gnd | 5 | Rx processor | 5 | Vpp | ||
| 6 | bit 3 | 6 | Mclr | ||||||
| 7 | bit 2 | ||||||||
| 8 | bit 1 | ||||||||
| 9 | bit 0 | ||||||||
| 10 | Gnd | ||||||||
| Board 3 Component list |
|---|
| C1: 470 uF C2: 10 uF C3, C4, C7, C8: 100 nF C5, C6: 22 pF C9: 1 uF R1: 33 K R2, R3: 4.7K R4: 1k U1: 7805, LM1086-5.0 or equivalent U2: PIC 16F873 or compatible, with 28pins socket D1: 1N4004 D2: BAT42 D3, D4, D5: 1N4148 LED1: led 5 or 3 mm Q1: 16 MHz (4 to 20 MHz) K1: Connector AMP MT 2pins male K2, K3, K4: Connector AMP MT 10pins male K5: Connector AMP MT 5pins male K6: Connector AMP MT 6pins male K7: pinheader 5 pins |
How to use / Testing:
To check the board, leave U2 out of its socket, and check voltage across pin 8 and 20, then 19 and 20 when the board is powered on. It must read 5V.
Check the power supply pins of the various connectors (K2 to K7).
To check the board fully, you need to fit the processor in its socket and run one of the tutorial projects (8 bits counter for example).
Files and links:
Eagle schematics file for board 3.Eagle pdf file for board 3.
PIC Tutorials.
Microchip PIC 16F873.
Posted at 2012-02-13 02:17:52
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