Summary of 50 MHz frequency counter, voltage meter & SWR/PWR indicator using PIC16C71
This article describes a successor to a PIC16C71 frequency counter, now utilizing a PIC16F876 microcontroller. The device measures frequencies up to 50MHz and power supply voltage from 0.0V to 25.5V. It features two analog inputs for displaying SWR/PWR signal strength on a bargraph with selectable sensitivity. Additional functions include automatic power save mode, programmable frequency offset, multiple display modes, and high resolution settings.
Parts used in the 50 MHz Frequency Counter Project:
- PIC16F876 microcontroller
- 4-digit LED display
- TO-92 style 78L05 voltage regulator
- Quartz oscillator (4,000 MHz or 4,1943 MHz)
- Analog inputs for SWR/PWR signals
| 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 |
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 A rather early PIC16C71 has also been replaced by 28-pin device PIC16F876.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:
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Measurement of the frequency up to 50MHz |
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Measurement of power supply voltage in the range of 0.0 V … 25.5 V |
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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. |
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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. |
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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 |
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Different display modes: XX.XX MHz, X.XXX MHz, XXX.X kHz |
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Display resolution 100 Hz |
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Measurement resolution 12,5 Hz |
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Hysteresis of displayed value 25 Hz |
For more detail: 50 MHz frequency counter, voltage meter & SWR/PWR indicator using PIC16C71
- What is the maximum frequency measurement capability?
The device can measure frequency up to 50MHz. - Can this project measure power supply voltage?
Yes, it measures power supply voltage in the range of 0.0 V to 25.5 V. - How are SWR and PWR signals displayed?
They are simultaneously displayed as a bargraph using two analog inputs. - Does the device support power saving mode?
Yes, it features automatic display shut-down after inactivity periods ranging from 3s to 240s. - Is a programmable frequency offset available?
Yes, an offset addable or subtractable from the measured frequency is settable between 0 and 99,999.9 kHz. - What display resolution does the counter offer?
The display resolution is 100 Hz with a measurement resolution of 12.5 Hz. - Can I choose different input sensitivities for the bargraph?
Yes, input sensitivity can be chosen between 0.25V, 0.5V, 1.0V, and 2.0V.
