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### Topic: AC (Read 3575 times)previous topic - next topic

#### james95

##### Jan 29, 2011, 11:44 am
I had a sensor who needs Ac in order to work.
What must I do in order to use AC with the arduino

#1
##### Jan 29, 2011, 11:46 am
James

a) Don't double (or even triple) post.
b) We need more info on the sensor, do you have a link to a spec sheet.

______
Rob

Rob Gray aka the GRAYnomad www.robgray.com

#### james95

#2
##### Jan 29, 2011, 01:01 pm
My question is how to use AC in the arduino.
The sensor is a conductivity sensor and i need AC in order that it works

thank you

#3
##### Jan 29, 2011, 01:52 pm
Quote
My question is how to use AC in the arduino.

Sorry mate but this doesn't make much sense.

If you want to switch AC under Arduino control you can do that with a triac or a relay.

______
Rob

Rob Gray aka the GRAYnomad www.robgray.com

#### james95

#4
##### Jan 29, 2011, 06:20 pm
it is a home made sensor to calculate the conductivity of water
when you have a disolution of water and for example salt (NaCl), and you transmit to it DC, the water suffer a process called desionization, because of that i must use AC in order that water do not deionizat and with AC water can transmit electricity, that is what i need to make the sensor works.
I think  this is the best explanation i can tell you about this part of my proyect

#### mk3

#5
##### Jan 29, 2011, 07:59 pm
james95, you really have not provided enough information... but I'll try to help by guessing what you want.

an example of an AC signal is sound, so you could try searching for anything related to getting a microphone signal into Arduino.  You could also search for single-ended opamp designs.  The principal is to put the average of your AC signal at 2.5V and this would typically be done with an opamp circuit.

I think study along those lines will lead in the right direction.. unless I misunderstand what you are trying to do.  I assume you wish to read an analog signal and that the signal is an AC one.

#### in10ceguy

#6
##### May 30, 2011, 06:53 am
I think it might be a good idea to consider this conductivity probe that does work with ardunio

http://webpages.charter.net/tdsmeter/conductivity.html

#### Grumpy_Mike

#7
##### May 30, 2011, 10:27 am
To make AC in this way use a H bridge circuit like you have for a motor. Then feed the direction control input with a signal that is at the frequency you want the AC.

#### rederikus

#8
##### May 30, 2011, 11:40 am
Obviously the Arduino will not work with an AC voltage.  It requires 7 - 12 Volts DC.

It sounds like your sensor is using low voltage AC to detect the water conductivity.  I hope that you are using a fully decpup0led transformer for this as AC mains (240V) + water + human can be fatal.

The Arduino analog inputs need a variable voltage beween 0 and 20V DC.  See here http://arduino.cc/en/Main/ArduinoBoardUno.

Can you please post a schematic of your AC based water sensor.  I'd like to see what sort of an output it presents to the outside world.

#### BillHo

#9
##### May 30, 2011, 02:29 pm
Here are one of the example of using microcontroller based conductivity measurement setup using 8031
A real time microcontroller based conductivity measurement setup
google--A real time microcontroller based conductivity measurement setup

#### rederikus

#10
##### May 30, 2011, 08:07 pm
@BillHo, If I were doing this project I would use the Wheatstone Bridge approach for the sensor/measurement device as defined in the pdf in the first result in your Google search.  This would provide a continuous and variable AC output which could be rectified and conditioned to provide the optimum voltage for the Arduino.  It couled even be opto-coupled to make absolutely sure that no mains voltavge could leak into the Arduino.

I actually used this method back ing the 1980s (no microcontroller, for a solar powered swimming pool heating system and it worked very well indeed.

The Arduino now has to sample and display the result.  You could use any ofthe oputputs to provide alarms and threshholds.

@james95, I'd still like to see the circuit that you are is using though.

#### Grumpy_Mike

#11
##### May 30, 2011, 11:54 pm
@rederikus
Quote
The Arduino analog inputs need a variable voltage beween 0 and 20V DC.

This is total and utter rubbish and is not supported by that link. Anything over and above the supply voltage to the chip on the analogue input will blow them up. So that is anything outside 0 to +5V.

#### elandd2011

#12
##### May 31, 2011, 12:13 am
I dont know if i got you
you have a home made sensor , you use AC to "power the sensor" and then read the output ,i suppose that the output is AC with same frequency ,ok
tell us AC value,i think is easy solution for low AC voltage

#### rederikus

#13
##### May 31, 2011, 10:42 am

I dont know if i got you
you have a home made sensor , you use AC to "power the sensor" and then read the output ,i suppose that the output is AC with same frequency ,ok
tell us AC value,i think is easy solution for low AC voltage

Mike, I ws amazed to see the quoted voltage inputs.  Imo this should be 5 volts max.  I was going to write just that when I thought that I had better check the manufacturers specs - as ya do.  I then just quoted what they said.

I am sorry to have given wrong information but after a lifetime in the electronics industy and a BSc to boot, I was very reluctant to misquote the manufacturer even though their numbers jibed with my own experience.

5 volts it is then

#### Grumpy_Mike

#14
##### May 31, 2011, 09:05 pm
Yes but where on that page does it sy that. You are not mixing up what it says about input voltage, that reffers to the power input at the DC jack.

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