Pulse counting for Gas meter using hall effect sensor

Submitted by charliemic on Sun, 08/12/2013 - 19:38

Evening,

I'm trying to set up an EmonTX for pulse metering (from a gas meter, with a magnet on the disk).

I have a hall effect sensor (TLE 4913);

http://uk.rs-online.com/web/p/hall-effect-sensor-ics/7533260/

I have soldered the jumper on the emonTX to give 5V.

I have NOT installed a 10k pull down resistor (I believe this is optional, on what basis should it be used?).

I have connected the sensor the the emonTX, and I'm using the sketch by Jerome (below). When I pass a magnet over the sensor, the serial monitor responds, but instead of showing a count number, it shows some random characters- see attached screenshot.

This doesn't seem right- any thoughts why it is doing this?

Chris

volatile unsigned int count;

void setup()
{
Serial.begin(57600);
Serial.println ("Start"); // signal initalization done

pinMode(3, INPUT); //set the interrupt0 pin3 to input
digitalWrite(3, HIGH); // and enable it's internal pull-up resistor

attachInterrupt(1, countP, FALLING); // device signals a low when active
delay(100);
}

void loop()
{

}

void countP()
{
count++;
Serial.println (count);
}

Re: Pulse counting for Gas meter using hall effect sensor

Submitted by MartinR on Sun, 08/12/2013 - 21:05.

Have you set the baud of your terminal window to match the 57600 in your sketch?

The default is 9600 if you haven't changed it.

edited to say: I just looked at your photo and noticed you do still have the baud set to 9600 so that's your problem

Re: Pulse counting for Gas meter using hall effect sensor

Submitted by charliemic on Sun, 08/12/2013 - 21:20.

Martin,

Thanks for that! Sorted now.

Chris

Re: Pulse counting for Gas meter using hall effect sensor

Submitted by Jérôme on Sun, 08/12/2013 - 21:47.

I have NOT installed a 10k pull down resistor (I believe this is optional, on what basis should it be used?).

Not my area so I won't try to explain. Search the web for "open drain".

The ATMega input is open drain. You use the (internal, because there is one) pull-up resistor to keep its input at Vcc and when 0 V is applied by the sensor, a falling edge is detected. You could use a (external, since there's no internal) pull-down resistor to keep it at 0 V and plug the sensors so as to send Vcc on the input when the magnet passes.

Actually what I wrote on my profile might be inaccurate:

Either connect it between GND and output and activate the pull-up resistor (tested), or just connect it between Vcc and output and don't activate the pull-up resistor (I suppose).

I don't know what happens if the internal pull-up is not active and if there is no external pull-down either.

I'm sorry, I think it used to be clear in my head, by the time I wrote it...

Anyway, I can't explain you clearly why, but you were right.

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