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Author Topic: Amplify DAC output to 0v-12v  (Read 3021 times)
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I am trying to use an arduino due to control the following http://www.vellemanprojects.eu/products/view/?id=354314 dc dimmer for an ac fan.

As far as I understand it the dimmer requires a dc input between 0v and 12v to control the ac fan with 0v stopping the fan and 12v for max speed.

I thought about using the DAC output and amplifying the dac output from the due.

Is this the right way to do it and how do I amplify the signal?

A quick search on Google makes me think that I need an op amp circuit to amplify the signal.  Can somebody point me to a suitable circuit for this or suggest a better alternative?

Thanks
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http://masteringelectronicsdesign.com/the-transfer-function-of-the-summing-amplifier-with-n-input-signals/

Add some DC to the other input if you need to add some offset.
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I am trying to use an arduino due to control the following http://www.vellemanprojects.eu/products/view/?id=354314 dc dimmer for an ac fan.

As far as I understand it the dimmer requires a dc input between 0v and 12v to control the ac fan with 0v stopping the fan and 12v for max speed.

I thought about using the DAC output and amplifying the dac output from the due.

Is this the right way to do it and how do I amplify the signal?

A quick search on Google makes me think that I need an op amp circuit to amplify the signal.  Can somebody point me to a suitable circuit for this or suggest a better alternative?

Thanks

May really not what you looking for but whats about an sperate IC for it like the AD5501BRUZ (12bit) or the AD5412AREZ (12-16bit) used SPI and take an seperate Voltage for the Output.
« Last Edit: June 04, 2013, 04:40:41 am by Markus_L811 » Logged

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I've recently been experimenting with something similar. I need to convert the DAC output range 0.55V-2.75V (approx.) to 0V-5V. So the DAC output needs to be offset by -0.55V and have a gain of about 2.3 applied. The best results so far are with a differential op amp circuit. I can feed the DAC into one input, +0.55V into the other and get an output in the range 0V-2.2V. The overall gain of the amp can be adjusted to give a maximum of 5V. There are lots of examples of differential op amp circuits online.

I prefer this to the summing circuit because I don't have -0.55V available.

BTW, I would recommend buffering the DAC output when experimenting with it. I managed to kill one of mine somehow. I think I've read that they are not very robust.
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I would use the PWM output, put it through a transistor to get it to 12V and then add an RC filter to smooth it.
Much simpler than bothering with analogue outputs.
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I looked at the schematic in the manual off the page you linked to. The input is via an opto-isolator with a 4.7K current-limiting resistor (R16). The other side of the opto-isolator there is an RC filter (1K / 10uF). I would suggest the following:

1) It is better to use PWM rather than the DAC because there is already enough of an RC filter in the circuit.

2) If you lowered the value of R16 from 4.7K to around 680 ohms then the input voltage range would lower from 0-12V to approximately 0-3.3V which would avoid the need for an amplifier.
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Thanks for your replies.

I will try stimmers idea number 2.

Thanks again.
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Thanks for your replies.

I will try stimmers idea number 2.

Thanks again.
Do not confuse 12 bits with 12 volts they are not the same thing.
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I've recently been experimenting with something similar. I need to convert the DAC output range 0.55V-2.75V (approx.) to 0V-5V. So the DAC output needs to be offset by -0.55V and have a gain of about 2.3 applied. The best results so far are with a differential op amp circuit. I can feed the DAC into one input, +0.55V into the other and get an output in the range 0V-2.2V. The overall gain of the amp can be adjusted to give a maximum of 5V. There are lots of examples of differential op amp circuits online.

I prefer this to the summing circuit because I don't have -0.55V available.

BTW, I would recommend buffering the DAC output when experimenting with it. I managed to kill one of mine somehow. I think I've read that they are not very robust.
Did you have a schematic for us to look at?
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No, I was just breadboarding it based on a standard differential circuit like this:

http://www.electronics-tutorials.ws/opamp/opamp_5.html

The op amp I used was MPC6002.

I used a pot to get 0.55V for V1 and fed the DAC into V2. 33k resistors throughout. In fact, I found that I had to increase the 0.55V to 1.1V to get the op amp output to be 0V for analogWrite(DAC1, 0). Haven't worked out the reason for that yet. Will try buffering the DAC output, looking at op amp errors...
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