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16  Using Arduino / Microcontrollers / How to support Serial Communications on a bare bones arduino on: September 22, 2013, 01:49:47 am
I have coded up a circuit using a bare bones Arduino as shown here.

I want to send data via a Serial port to a computer.

I have a USB to Serial adapter - Similar to the following

Is this enough to support Serial Communications or do I need to do something else?  Sorry for the lack of detail but I really do not know what is required.

Any help appreciated


17  Using Arduino / General Electronics / Re: CT Clamp and AC to DC on: September 17, 2013, 02:59:23 am

Are you sure that the voltage is enough to drive the first diode?

My ac voltage from the CT Clamp is only 0.023v for a 1000w load on the CT clamp at 240v.

I do not think this is enough to drive the Diode to rectify the AC signal?

I am going to do some playing around with a Software Circuit Tester to see if this will work.

18  Using Arduino / General Electronics / Re: CT Clamp and AC to DC on: September 15, 2013, 08:41:29 pm
A colleague at work suggested that maybe a Toroidal current transformer may be a better thing instead of a current clamp since my current is quite small - generally 1000w would be the maximum.

I am going to look into this and see how I get on.

19  Using Arduino / General Electronics / Re: CT Clamp and AC to DC on: September 15, 2013, 06:52:29 pm
I guess accuracy as good as a plugin power monitor like you can buy for $20 would be good.

Form my simple test with the clamp as I said in the first email I received:

0.023v from 1000w load
0.046v from 2000w load

All I really want to do is convert the small AC to DC and then after that conversion amplify the signal so it is between 0 and 5v - so something like a 100X Multipler.

The article I referred to in the first post shows the following diagram:

I am just not sure on the final two components a resister and capacitor I assume to filter the signal, but I do not know how to calculate this.

The pdf has this text

  • The CT secondary current is applied to the resistor R1, which generates a voltage equal to the primary current
    divided by the turns ratio and multiplied by the value of R1. This AC voltage is rectified by the first op amp,
    and then amplified by the second op amp.  
  • The gain of the first stage is always kept at 1 or unity (R2 = R3) to guarantee symmetry of the rectified
    waveform. R2 should be chosen at least 10 times greater than R1 for proper accuracy.  
  • The gain of the second stage is R5/R4 + 1. This gain is chosen to get the desired output DC voltage for the
    designed input voltage.  
  • The main advantage of this circuit is the removal of the diode drop as a variance in the signal. DC can be
    generated directly from R1 by applying the AC voltage to a diode bridge. However, the AC voltage required to
    do this must be greater than 2 diode voltage drops, or over 2 VAC. This limits the designer to use a silicon steel
    core that can generate enough voltage before going into saturation. By using the above circuit, the AC voltage
    input can be very low (10-100 mV) and then amplified to the level desired. This then allows the designer to
    choose smaller core devices and nickel core devices which saturate at low voltages. Accuracy and cost are both
  • Use standard op amp design guidelines when setting up this circuit. Keep resistors at 1 M ohm or less, and
    keep gains to 100 or less.  
  • The output must be filtered for pure DC. The RC output network shown should be designed with a time constant
    at least 10 times greater than the period of the waveform sensed. For 60 Hertz, use a time constant of 1/6.
    For 400 Hz, use a time constant of 1/40, minimum.

So for me I am thinking of using

Z1, Z2 = 1N4735A  - not sure if this Zener is OK, 6.2v 1W but I assume it is.

R1 = 10 Ohm
R2 = 100 Ohm
R3 = 100 Ohm
R4 = 1k Ohm
R5 = 100K Ohm (to give a 100 x multipler)

R6 = ?
C1 = ?

Technically with my 100 times multiplier I believe:

0.023v * 100 = 2.3v
0.046v * 100 = 4.6v

So I should be able to read this on an analog in on the arduino?

20  Using Arduino / General Electronics / Re: CT Clamp and AC to DC on: September 14, 2013, 11:51:08 pm
I am wanting to monitor it over time using my Arduino....

So these devices you refeered me to are good, but I simply want to monitor it using some simple circuit and log it to a database.

21  Using Arduino / General Electronics / Re: CT Clamp and AC to DC on: September 14, 2013, 11:35:31 pm
Complete control but no knowledge of how much power is consumed!

Since the filters and the air are on 24x7 and the lights are on at 7:15am and off at 8:45pm they are automated.

The heaters are on an off as required to keep the tank warm, which changes per day and per month.

So at the end of the day I am interested in how much this is costing me to keep running not controlling it!


22  Using Arduino / General Electronics / CT Clamp and AC to DC on: September 14, 2013, 09:46:21 pm

I am wanting to monitor my aquarium power usage, this will be on a New Zealand 230v, 50 hz system. It all runs from a single power point.

In my setup there is the following:

  • 2 Filters - about 10 watts
  • 2 heaters - potentially 600w if both are on
  • Lights
  • Air

So I am wanting to use the CT Clamp with produces via a burden resister an AC voltage.

In my testing with a 1000w/2000w fan heater which would draw close to 5 Amp at 1000w

Now running the heater at 1000w I see an AC voltage of 0.023, if I switch the heat to 2000w it jumps to 0.46 volts AC

I have been looking around and playing with some circuits to try to convert this to DC. At the moment I am running this on a multimeter but I want to use an Arduino to save this data.

Since the voltages are so low what are induced from the CT Clamp I am thinking of a precision rectifier circuit to convert to DC. I would like to make 10amp = 5v.

So 5 amp (heat running at 1000w) = approx 2.5 volts.

Looking at there was a comment that pointed to a PDF at

I have tried to follow along but I am confused.

The diagram mostly makes sense and the description.

But there is a Capacitor and a Resister on the right edge of the diagram that I do not know what to use.

Also the diagram has two inputs from the CT Clamp - but only 1 output - and this confuses me as well.

If I run the LM324 (or LM528 in my case) from 5v so I use the ground from the power supply source?


23  Using Arduino / Sensors / Re: Trying to control Mitsubishi Heat Pump Air Conditioning Unit on: September 05, 2013, 11:03:37 am
Thanks for the web site - I may look into that.


24  Community / Exhibition / Gallery / Re: Solar power for your arduino on: September 03, 2013, 12:37:21 pm
Great, keep them coming....

25  Using Arduino / Sensors / Re: Trying to control Mitsubishi Heat Pump Air Conditioning Unit on: August 20, 2013, 12:49:52 am
Hi Guys

I can not longer help with any details on this project as my Mitsubishi died - $2000 NZD to fix - so it is not getting fixed.

All that for a fan and a fuse!

What is the point of a fuse if it blows you have to replace the whole circuit board- sounds like a con to me!

26  Community / Exhibition / Gallery / Re: Solar power for your arduino on: August 04, 2013, 03:56:37 am
Can't wait fr some more articles - good

27  Using Arduino / Sensors / Arduino PH Meter for Aquarium - What is the best/cheapest option on: July 20, 2013, 10:39:40 pm

I am wanting to implement an Arduino PH Meter and I know there are a lot of these out there that people have made and some details published online.

Is there a good cheap product(s) that can be recommended?

From what I can see I need an Arduino + a PH Meter board + a Ph sensor normally BNC connector. Is there a specific type/quality I should look for?

Can all ph sensors be permanently placed in an Aquarium? What happens if they are not suppose to be permanently submerged and they are?

I do not have a reef aquarium but a simple Community Tank - about 300 litres.

I have done some searching and there are a number of products that people mention but is there a known good set of products that people can recommend?

Do you need to buy calibration liquid? Or do some support not needing this? or is this bad?

Circuits for Arduino - About $28 + Shipping (stupid shipping price on Ebay) - $30 + Shipping (not yet checked price to NZ) - $38.55 shipping  (not yet checked price to NZ)

PH Sensors (BNC) = $25 + shipping (not yet checked price to NZ) - $9 incl shipping - Quality?

I know there are lots of different products but is there any recommended products from people who have already done this?

28  Using Arduino / Sensors / Re: Using a Piezeo Element to read analog values on: July 19, 2013, 08:59:34 pm
OK I have found that if I put a 1M resister between the Red + Black legs of the Piezieo element then I get good data.

Thanks for the info on the knock sensor - it helped but I found it on a youtube video and not on here.


I have also changed the loop to

void loop() {
  // read the value from the sensor:
  sensorValue = analogRead(sensorPin);  
if (sensorValue >= 5)  
  // turn the ledPin on

So I now have

A0 connected to 1 Leg of 1M resister and then connected to RED leg of Piezo
GND connected to other leg of 1M and then connected to BLACK leg of Piezo

29  Using Arduino / Sensors / Using a Piezeo Element to read analog values on: July 19, 2013, 07:35:54 pm

I am using an UNO and a piezeo element connected directly between ground and A0

The additional wires (red + orange) are only being used to hold the very small Piezeo wires in place - nothing else.

My code is


int sensorPin = A0;    // select the input pin for the potentiometer
int sensorValue = 0;  // variable to store the value coming from the sensor

void setup() {
  // declare the ledPin as an OUTPUT:
  pinMode(ledPin, OUTPUT);  

void loop() {
  // read the value from the sensor:
  sensorValue = 1023-analogRead(sensorPin);    
  // turn the ledPin on


This runs full speed and generally returns 0 if nothing is going on. But if I touch/tap the piezeo element it changes values say jumps to 600 and then slowly reduces back to 0.

This reduction to 0 can take 30 seconds.

I would have expected a much quicker drop to 0

If I was using this to record audio (such as a rain drop or hail) I would need much quicker reduction to 0 since one strong hail stone would be only a few ms not 30 seconds.

Any ideas on what I need to ensure a quicker drop and why it is doing this?

Could there really be that much energy being released over 30 seconds?

30  Community / Products and Services / Re: Xboard Relay: making Internet Of Things easy (iphone ready) on: July 09, 2013, 02:31:09 pm
You say the relay board is discounte to $17.00 but your web site does not offer this price!

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