Hans Summers wrote:
Hello

I have built 2 very simple 2-chip frequency counters with 8 LED binary
readout see http://www.hanssummers.com/radio/sfreq/index.htm . My Mk2
counter is extremely small (just 25 x 16 x 16mm) and consumes a low current
of 5mA max.

The question relates to the 4.096MHz oscillator which uses the internal
oscillator of the 74HC4060. Of the 5mA current consumption, 1.2mA is used by
the LED's when max 7 are on at any one time. About 0.8mA by the
diode-resistor gate logic, transistor switch, 74HC4040 and the voltage
regulator. Fully 3mA is wasted on the 74HC4060 crystal oscillator + divider.
It seems wrong to spend 60% of your current consumption on an oscillator,
compared to less than 25% on the LED's.

In the pursuit of excellence in this design, I would like to cut the current
consumption of the oscillator section. Does anyone know of a better
arrangement that will cut current consumption? Increasing the series
resistor wasn't the solution. I put a 100K variable in here in place of the
original 2K2. Initially as the resistor was increased the current
consumption fell, but at higher resistances the current consumption
increased quite dramatically. The optimum was at close to 4K7.

73 Hans G0UPL
http://www.HansSummers.com




On the other hand, you can always console yourself with the fact that
60% of your power budget is going toward making the thing accurate...

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com