polar heart rate monitor « Jee Labs Talk

polar heart rate monitor

(10 posts) (4 voices)

Tags:

No tags yet.

lordmundi

we are hooking up the Polar Heart Rate monitor (HRMI) circuit from SparkFun and Dan Julio. We are trying to talk to it over I2C and have been at it for quite a few days with no success.
We have unsoldered SJ1 and soldered OP7 as directed to in the manual. We have also tried with and without external pull up resistors (I don't know if the JeeNode automatically has pull-ups or not). We have even tried soldeirng OP7 since the default address of 127 seems to be a reserved address in the I2C standard.
All with no luck. We get garbage back.
For wiring, we have:
HRMI JeeNode
+5V P
GND G
SDA D
SCL A
Has anyone ever hooked up this circuit to a JeeNode before? We are trying to use the Ports library and the I2C functions since these are so easy to understand, but we have been trying every possible placement of device.stop() and device.send() and device.receive() calls since we don't quite know where they go for sure. We've gotten the TMP421 temperature chip working and have based our code off of that. I can post the code, but was just mainly interested if anyone else has ever done this, or if anyone sees any issue with the way we have the hardware configured.
thanks for any help!
FG

Posted 24/07/2010 22:08:57
stef007

It looks like your HRMI "sensor" is running at 5V? I suppose the voltage levels on its SDA and SCL are also 0-5V? If so, it's not going to work because JeeNodes run at 3.3V and also expects its signals to be 0-3.3V.

Posted 25/07/2010 12:02:13
lordmundi

wow... i was just looking into that when i saw your reply. that's what I was afraid of! ok, so, if this in fact the issue, any way to get my JeeNode to run off of 5V? Can I bypass the regulator somehow and power it with my own regulator then change my USB-BUB to operate at 5V?
FG

Posted 25/07/2010 14:38:31
stef007

Can't help there sorry. But I would watch out: the RF12 does not like 5V, although the atmega can take it.

Posted 25/07/2010 15:25:56
epokh

You can use a logic (level shifter)http://www.sparkfun.com/commerce/productinfo.php?productsid=8745], also sold on sparkfun and provide a separate 5V supply for the polar monitor.

Posted 27/07/2010 12:32:39
rowfast

Thanks, this is also helping my project. http://talk.jeelabs.net/topic/70#post-2333

Posted 28/07/2010 19:15:20
rowfast

Would this work? a Step-Up Breakout like this http://www.sparkfun.com/commerce/productinfo.php?productsid=8999? anyone experience with it or similar? Thanks!

Posted 28/07/2010 20:47:31
lordmundi
well, after some experimenting, I was able to get the board up and running with the example code from Dan Julio. I think this proves that the logic levels are ok (Dan suggested they should work with 3.3V and after this test, it seems it should).
To get his example code to work on the jeenode, I had to wire up to the SDA and SCL lines on the PSI port instead of trying to make an I2C port using one of the Jeenode "Ports". This let me run his code pretty much unmodified except for having to change the I2C address to one that matched the jumpers I have soldered on the board.
But, one big obstacle still remains. This lets me prove the board works, and works over I2C and works with the Jeenode. But for the life of me I still can't seem to get this to work using the Ports library (which I wish I could). Keeping the HRMI wired to the PSI port, I used "Port 0" as it looks like JC has made the Ports library map port 0 to the Arduino hardware I2C lines. I thought that the main issue was the clock rate on the I2C bus, but even with setting this to 9 in the constructor, still getting garbage from the Port. I've tried lots of stuff but obviously I'm still missing something. The code is below. Can anyone suggest why this hardware works with the wire library but won't work with the Ports library?
```
    #include 
    #include  // needed to avoid a linker error :(
```
```
    PortI2C myport (0, 9);  // the default clock may be too high. use 100 KHz
    DeviceI2C hrmi (myport, 0x3f);  // address for pin OP7 soldered
```
```
    void setup() {
	Serial.begin(57600);
	Serial.println("\nHRMI;
    }
```
```
    void loop() {
```
// request 1 reading (3 bytes total) hrmi.send(); hrmi.write('G'); hrmi.write(1); hrmi.receive(); byte value1 = hrmi.read(0); byte value2 = hrmi.read(0); byte value3 = hrmi.read(1); hrmi.stop();
Serial.print(value1, DEC); Serial.print(" "); Serial.print(value2, DEC); Serial.print(" "); Serial.println(value3, DEC);
delay(1000);
```
    }
```
Posted 30/07/2010 03:02:01


	
		
			
								
					stef007

				
			
			
				
If you set the rate to 9 the i2c port code will use a delay of 9 microseconds. This calculates to 111 Khz. According to the HRMI docs the highest rate supported is 100Khz. You're cutting it close (or to much;-)). I suggest passing something safe as rate/delay for example 100 which would translate to 10Khz?
Also did you see Dan suggests that pull-up resistors might be necessary? Perhaps you could try that also if you haven't already.



				Posted 30/07/2010 09:24:49
			
		
	
	
		
			
								
					lordmundi

				
			
			
				
thanks so much for all your help.  unfortunately, I tried setting the rate delay as high as 20 (not the 100 you suggested but something that should definitely fix the issue), and there was still no change.  Also, I tried with the pull-up resistors as Dan suggested.
For now we may punt and just use the Wire library with this hardware since figuring this out appears to be eating away at our schedule.  If anyone else gets this working on a soft I2C on a Jeenode, PLEASE let us know how you did it!



				Posted 30/07/2010 13:46:20