Frequency Generator with 2x Variable Resistors

Hi Shaun,

I think the Arduino is the wrong part for this. The result won't be great, there will be granularity issues and furthermore jitter due to noise in the VR1/2 value read (unless digitally filtered which means more code and some latency).

There are easier solutions like this one, see the datasheet for detail:

http://www.linear.com/product/LTC6992-1

For the inverted output, one idea is to use an inverter logic gate IC.

An alternative way using easy-to-obtain parts (but a bigger circuit) would be to generate a triangle or sawtooth wave under control of a variable resistor, and then use a comparator to convert to pulses (with a second variable resistor controlling the pulse width by changing the comparator threshold).

Although I cannot design the circuit for you, for an idea, see the circuit here: Raspberry Pi enabled Christmas Lights

By changing the value of R1 in the sawtooth generator circuit there, you can change the frequency (this is equivalent to your VR2).

The circuit below that on the same web page shows the comparator acting as the PWM generator, controlling the pulse width.

... using rotary encoders instead of potentiometers could help here. You can then define both their range and dynamic behaviour in the source code.

You could refine the output with huge chunks when the encoder is turned fast, and small steps when turned slow.

Sounds simple.

There are a couple of ways to do the 'opposite pin' thing.

You'll need to drive the valve with a transistor or Mosfet regardless of what method is used.

Unless you have something else you haven't specified, the 'other' valve will always be opposite.

This hardware could include the second output that is opposite in phase (ie off when the driver/pin1 is on).

Regarding your analogue input, you simply have to specify the range of control.

I think you commented 0.1sec (10Hz) to 5 secs.for the 'cycletime', but you've only said it should be on for 100-200mS.

If the 'cycletime' is 0.1Hz which is 100mS, and the duration is 100mS, it would be ON all the time ... presumably not the intention.

.

Let's presume the timing doesn't need to be accurate, then a potentiometer is fine.

You can easily use the MAP command to change the 0-1024 value you'll get from the AnalogRead command and use it to control the on time/duration time.

0.1 is 100mS and 5 secs is 5000mS which is a normal integer.

I don't have the IDE here, but I would map 0 to 100 and 1024 to 5000 or the other option is 0 to 5000 and 1024 to 100.

MAP is a linear conversion, but you can use a logarithmic potentiometer which has a non linear characteristic to make it seem more even.

An example exists in the IDE.

Blinkwithoutdelay uses the millis() timer and would be what I'd suggest.

You'll have two seperate timer variables, one for 'cycletime' and the other for 'duration'

Hope this helps start you out.

You'll need to fill in the blanks I mentioned.

Cheers

Mark

.

It sounds like a dual 555 timer chip (556) could perform all the timing you need - variable duty cycle at a variable frequency.

They can operate up to 15 Volts, so should run off the same supply as the solenoids.

Driving solenoids in opposite phase is as simple as connecting them in series across your supply and driving the connection between them high or low with a class B transistor pair.

Don't forget to put snubber diodes across your solenoids.