BINARY DECIMAL LED DISPLAY VERSIONS OF THE SIMPLE FREQUENCY COUNTER


Posted on Feb 6, 2014

There are other display methods than the original 8 led frequency counter has. They are perhaps easier to read and may have a format that fits better to the front of your QRP equipment. Here some examples of binary decimal displays are given. Mostly the the counter is made without the MHz position, only the kHz position is used to read the VFO fre


BINARY DECIMAL LED DISPLAY VERSIONS OF THE SIMPLE FREQUENCY COUNTER
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quency within a 100 kHz segment. This counter uses only 7 leds for reading the frequency in a 100 or 50 kHz segment. The counter starts counting at zero at each multiple of 100 or 50 kHz. Gating is done after the first /2 divider. In this version, also the preamplifier is deleted and 74HCT390 chips are used instead of a 74HC390 for maximum sensitivity. The first /2 divider is adjusted for maximum sensitivity with a DC bias voltage. Gating is done after this first /2 divider. Of course it is also possible to use 74HC chips plus the RF preamplifier. In this case, the RF preamplifier is supplied by the 5V supply and not by the gating pulse. The advantage is that the RF amplifier is not switched on/off by the gating signal which might influence your VFO frequency due to the varying load. The least significant led (2 or 1 kHz) works like an analog scale. It slowly varies in brightness when the frequency is changed. Therefore, the frequency reading is much better than the value of that led. The 74HC4040 in the original 8 led counter is replaced by a 74HC390. This chip has two /10 dividers so that we will have that new display with 2x4 leds instead of the 1x8 led display. A 74HC00 (do not use a HCT) is added, one NAND is used as RF preamplifier to increase the sensitivity and as buffer between the VFO and counter, another as an RF gate switch to start and stop the counter. The unused inputs of the two remaining NAND`s are...




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