[time-nuts] Local Solar Time Clock

Jim Lux jimlux at earthlink.net
Sun Jan 19 13:58:16 EST 2014


On 1/19/14 10:11 AM, Chuck Harris wrote:
> Given the relatively low currents needed by the clock
> motor, and the relatively high currents that can be
> sourced/sinked by the arduino, and the fact that the
> motor winding is floating relative to the arduino,
> one could probably connect the motor like this:
>
> D0---SomeResistor--MOTOR-----D1
>
> Then, how to describe the way to drive it?
>
> Well, starting out with D0=D1=0,
>
> Set D1=1, then in 0.1 sec set D0=1.
>
> Wait 0.9 sec then:
>
> Set D0=0, then in 0.1 sec set D1=0...
>
> Wait 0.9 sec then:
>
> wash rinse repeat...

That's what I'm going to try.

Actually, on an arduino, you can set the output pin to Hi Z..

So it's more like
#define PulseLength1 100		// milliseconds
#define PulseLength2 100
void ClockTick(){
	digitalWrite(D0,LOW);		//preload the bits
	digitalWrite(D1,HIGH);
	pinMode(D0,OUTPUT);		// now make them an output
	pinMode(D1,OUTPUT);
	delay(PulseLength1);		// wait til pulse first part
	digitalWrite(D0,HIGH);		// flip direction
	digitalWrite(D1,LOW);
	delay(PulseLength2);		// wait til second part
	pinMode(D0,INPUT);		// turn off pulse
	pinMode(D1,INPUT);
}

That way you're not drawing power most of the time..




>
> -Chuck Harris
>
> Jim Lux wrote:
>> On 1/19/14 9:17 AM, Chuck Harris wrote:
>>> The usual quartz clock that runs off of a AA cell is a little
>>> trickier to drive than you might think.  You need to feed
>>> its stepper motor coil with an alternating +1.5V and -1.5V pulse.
>>> The pulse follows the rising or trailing edge of a 1/2 Hz square
>>> wave.  I have driven them using a series capacitor and resistor
>>> to ground...arranged as a differentiator, but I don't recall the
>>> part values anymore.
>>>
>>> You arduino could certainly be made to generate such a pulse using
>>> a couple of resistors and a couple of digital outputs in a simple
>>> DAC sort of circuit.
>>>
>>
>> Yeah.. that *is* the challenge.
>>   Use two outputs and make a sort of "H bridge"
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