Summary of 50 MHz frequency counter, voltage meter & SWR/PWR indicator using PIC16C71
This project is a 50 MHz frequency counter, voltage meter, and SWR/PWR indicator using the PIC16F876 microcontroller. It improves upon its predecessor by eliminating obsolete parts and integrating LED driving and EEPROM functions into a single chip. The device measures frequency up to 50 MHz, power supply voltage (0-25.5 V), and two analog input voltages displayed as a bargraph for signal strength. Features include selectable input sensitivity, power-saving display shut-off, programmable frequency offset, multiple display modes, and high measurement resolution.
Parts used in the 50 MHz frequency counter, voltage meter & SWR/PWR indicator:
- PIC16F876 microcontroller (28-pin)
- 4,000 MHz crystal oscillator (for HEX code V1.11)
- 4.1943 MHz crystal oscillator (for HEX code V1.12)
- 4-digit multiplexed LED display
- Voltage regulator (78L05 in TO-92 package)
- Push-button switch
- Analog input components (resistors, capacitors as required)
- PCB board (latest version as shown)
- Supporting passive components (resistors, capacitors)
| Circuit schematic | PCB | HEX code, V1.11 (operates with 4,000 MHz quartz) | Hex code, V1.12 (operates with 4,1943 MHz quartz) | PIC config bits |
| Photo – Top view | Photo – Bottom view | Photo – Latest PCB version with TO-92 style 78L05 housing – Top view (132 kbyte) | Photo – Latest PCB version with TO-92 style 78L05 housing – Bottom view (138 kbyte) |
This is a successor of the PIC16C71 4-digit LED f-counter & V-meter. Some hard to find parts used in the previous version, which are out of production for some time, has been omitted. A rather early PIC16C71 has also been replaced by 28-pin device PIC16F876. The later is capable of driving 4 digit LED display in multiplexed mode while measuring frequency, power supply voltage as well as handle two analog inputs to display SWR/PWR signal strength in a bargraph manner. There is no need for external LED display driver chip as well as external data EEPROM since it is already implemented in PIC16F876. Reduction in the number of used chips also results in smaller dimensions of the counter compared to its predecessor.
The latest software version (V1.1) supports following functionality:
 | Measurement of the frequency up to 50MHz |
| Measurement of power supply voltage in the range of 0.0 V … 25.5 V |
| Measurement of the input voltage at two analog inputs, simultaneously displayed as bargraph (PWR/SWR or S) indicator. The input sensitivity could be chosen between 0.25V, 0.5V, 1.0V and 2.0V for maximum bargraph indication. |
| Power save mode: Automatic display shut-down in case the push-button action or frequency change does not occur for a certain time. Display switches on againt after frequency change or push-button action. The available shut-down time periods are 3s, 10s, 30s, 60s, 120s, 180s and 240s. This function can be disabled in set-up menu. |
| Programmable frequency offset added or subtracted from measured frequency, settable in the range of 0 to 99,999.9 kHz. This is convenient for use with heterodyne type of RX/TX |
| Different display modes: XX.XX MHz, X.XXX MHz, XXX.X kHz |
| Display resolution 100 Hz |
| Measurement resolution 12,5 Hz |
| Hysteresis of displayed value 25 Hz |
For more detail: 50 MHz frequency counter, voltage meter & SWR/PWR indicator using PIC16C71
