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





Not familiar with the chips you are using but you should use the lowest
frequency oscillator possible.
Maybe try the 32 + KHz crystal

A lot of the current is used to charge and discharge internal capacity
so doing that less often helps.

Bill K7NOM

"Bill Janssen" wrote in message
...
Hans Summers wrote:

[snip]



Not familiar with the chips you are using but you should use the lowest
frequency oscillator possible.
Maybe try the 32 + KHz crystal

Bill, I am aware that CMOS current consumption is dependant on operating
frequency. However the simplicity of the design demands a clock frequency
which is a power-of-two multiple of 1KHz. Otherwise the counting range would
have to be other than 0 to 99.5KHz. This counting range is perfect for
amateur bands, the offset off the band edge or next multiples of 100KHz.

In any case the counting frequency of the 74HC4040 in my tests was very
similar to the 74HC4060 timebase since I was using an 80m VFO. But the
current consumption of the 74HC4040 was negligble. Therefore there must be
something about the oscillator configuration which is causing the high
current consumption.

That's why I'm wondering if there are other, more power-efficient ways of
making an oscillator. Bear in mind that a 32768Hz watch crystal is only 125
times slower than my 4096KHz crystal. Assuming proportionality that's about
25uA. Isn't this rather large for a watch? What sort of capacity are we
looking at in a watch battery... 25mAh or less? In this case a watch battery
would only last 6 weeks, and that's just powering the oscillator on its own
not even worrying about the watch hands.

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