June 2005, Issue 179

Precision Frequency Meter
Cypress PSoC High Integration Challenge 2004 Contest Winner

SYSTEM PERFORMANCE

Overall the system works well. You can accurately measure frequencies up to approximately 250 kHz. After the radio is tuned and free from noise, the meter recognizes the time pips and adjusts itself accordingly. The only time it will fail is when the radio commentators talk over the pips!

The oven works properly. There’s a ±0.3°C ripple in the case temperature, but it isn’t visible on the internal sensor. The internal sensor is approximately 2.5°C below the case temperature. (This is unexpected because I thought the air in the case would eventually match that of the case.) Possibly because of the position of the sensor and heaters, the temperature isn’t the same over the entire case. Thicker walls would probably fix this. But this temperature difference isn’t important because the reference oscillator remains at the same temperature. There might be small variations during the day depending on the room’s temperature. The actual accuracy of the reference frequency shows some initial variation, but as the number of hours accumulates in the clock rate register, the reference frequency remains constant.