Polar Heart Rate Monitor

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adafruit_support_bill
 
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Re: Polar Heart Rate Monitor

Post by adafruit_support_bill »

Can't really see how things are connected in the photo.
HRM = pin 9
LED = pin 8
Might want to try some more widely separated pins.

daz1761
 
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Re: Polar Heart Rate Monitor

Post by daz1761 »

Hmm, yes it seems to be as stable as it was without the LED code now after moving the LED pin to pin 6. I'm a little confused why it played up when I had the HRM and LED pin right next to each other?

Its quite ironic as I can barely see the LED light on and off when logging data now, but any feedback is better than nothing.

Do you think I should leave the LED code out? Is executing the 2 'if' statements likely to imperil the timing of the pulse function?

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Re: Polar Heart Rate Monitor

Post by adafruit_support_bill »

The if statements shouldn't take much time to execute relative to the beat period. If the problem goes away by moving the signals to different pins, then the cause is most likely some noise. How are you powering the pulse rate receiver?

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Re: Polar Heart Rate Monitor

Post by daz1761 »

At the moment I'm using a FTDI 3.3v adapter. When its built into a box I'll be using one of your 3.7v 1200mah LiPo's. I thought there wasn't any noise when using digital signals?

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Re: Polar Heart Rate Monitor

Post by adafruit_support_bill »

If you are powering the receiver with 3.3v, the output signal will be 3.3v logic. 3.3v is just above the logic HIGH threshold for a 5v Arduino, so the Arduino will recognize digital signals from most 3.3v devices. But if the signal is marginal, it will be more easily affected by noise.
I thought there wasn't any noise when using digital signals?
There is always noise. As long as the digital signal is stronger than the noise, the circuit will ignore the noise. But that is not always the case.

daz1761
 
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Re: Polar Heart Rate Monitor

Post by daz1761 »

I see, thanks.

I don't believe it! My setup is perfect through the serial monitor. Just took it into another room and tried it with the 3.7v lipo, just opened the the .csv and the signal is all over the place! Completely unsteady and noisy :-(

Just an update: Ive disconnected the Pololu 5v step-up and everything is stable again.

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Re: Polar Heart Rate Monitor

Post by adafruit_support_bill »

Can you post a photo or diagram of the whole setup?

daz1761
 
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Re: Polar Heart Rate Monitor

Post by daz1761 »

Sorry, yes here is a basic one I have just quickly sketched up.

Its only when powered using the 3.7v LiPo I get issues. For now I have disconnected the 5v stepper and DS1307.
Attachments
Basic Diagram.png
Basic Diagram.png (28.24 KiB) Viewed 297 times

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adafruit_support_bill
 
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Re: Polar Heart Rate Monitor

Post by adafruit_support_bill »

It's hard to say. Boost converters are switching regulators and another possible source of noise. Check the supply voltage when powered by your 3.7v LiPo . If the voltage drops significantly under load it could also cause problems.

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Re: Polar Heart Rate Monitor

Post by daz1761 »

The voltage does seem to drop quite considerately. Mission aborted, will have to build it without the DS1307 for now. I may post something on the Pololu forums about the stepper at some point.

Off the topic slightly, would you know if it is okay to widen one of the two pin holes on the actual module. The holes seem to have a diameter of under 1mm, very small. I wanted to widen the hole nearest the pins to 1.5mm so I can fit a M1.2mm small bolt through it. The second hole right next to the sensor itself looks too close for comfort to start drilling. Obviously I don't want to drill over any circuits, although there doesn't seem to be any close to the former hole.

I've attached a diagram to explain.
Sensor.png
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Re: Polar Heart Rate Monitor

Post by adafruit_support_bill »

I don't have one here at the moment, but from the photos on-line there does not appear to be any circuitry in the vicinity of either hole. It should not be a problem to widen them.

daz1761
 
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Re: Polar Heart Rate Monitor

Post by daz1761 »

Thanks. Yes I drilled it to 2mm wide and all is good :)

I did find another stepper (adjustable) that is supposed to work with a single cell 3.7v LiPo, but sadly it would of been nearly £15 with postage, so I have left it out on this occasion.

Do you think you will stock anymore biometric stuff? Would be great if you sold an equivalent quality GSR (galvanic skin conductance) kit.

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Re: Polar Heart Rate Monitor

Post by adafruit_support_bill »

Would be great if you sold an equivalent quality GSR (galvanic skin conductance) kit.
Thanks for the suggestion. I will forward it to the product team.

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