Temperature Logger and Buzzer

[kim27]

My family has started incubating eggs, and it has been a real struggle to keep the temperature in the right range. Perhaps it is the incubator, perhaps user error. At any rate, I wanted to lend a hand with my technical know how, so I have begun working on a project. I'm still in the beginning stages, but here is the basic concept. I want to create a temperature logger to store data for the entire period of incubation, and also an alarm or buzzer for when the temperature is too far out of bounds. Here are the results for three days of incubating.



The temperature is in F multiplied by 100. Basically 98.00 degrees equals 9800. (In microprocessors it is cheaper to do math as whole numbers instead of decimals; Although, I could probably modify the data after I get it into my computer)

For the project I'm using the MSP430 with factory calibrated temperatures. The ADC in the MSP430 is a 10bit ADC, but is only sensitive to about 0.5 degrees C. To increase the sensitivity, I'm using oversampling to get about 13bits of accuracy. I then use Integer math to convert the temp to F with two decimal places. I check the temperature every 10 seconds and alarm if the temp is to high or too low.

Right now the data logger is storing temperature at about 15 minute intervals. I need to add a crystal so that I can measure this more precisely, as the times right now are approximate.

The buzzer / alarm is proving a bit problematic for me. Right now, I have a 70 dB buzzer, but it seems to quiet. Any thoughts about what dB would be good for an alarm? (I know I am probably asking in the wrong forum, but I figured you may all enjoy my nerdy build and following along with my progress and frustration.) The challenge is finding an affordable buzzer that is easy to drive at ~3 V.

The other problem I have is battery life. I'm currently using one or two CR2032s( http://en.wikipedia.org/wiki/CR2032_battery ). When I'm using one battery should last two or maybe three incubations. When I'm using two batteries I need to regulate the voltage, but the current voltage regulator I'm using uses too much power, so battery life is estimated to be roughly 30 hours. The two battery approach may be needed to keep the buzzer well powered. I'm looking at a new LDO voltage regulator, and that should take care of the problem.

Finally, is anyone else concerned with the temperature ranges that the incubator is running at? ( Finally, a chicken question! ) I may need to do some more testing to make sure that the thermostat is behaving inside of my logger, but I'm feeling relatively confident about it.

I'll put some pictures up of my temperature logger as I progress. Right now it is in the prototype stages on a breadboard.

Kim

 

[Mister B]

What voltage is your buzzer rated? I have some 12v buzzers that will sound sickly when operated at 3-6v. they are something like these: http://www.rapidonline.com/audio-visual/hcm1212x-miniature-buzzer-12v-35-0056. ( I bought mine elsewhere, this is just for picture purposes) I was using it for a rocket launcher to denote when the "Arm" button was pressed. It was weak sounding at 9v, but perked up when I changed to a 12v battery.

 

[kim27]

The buzzer is PS1740P02E. The datasheet is here http://www.tdk.co.jp/tefe02/ef532_ps.pdf

From the datasheet is looks like it is rated at 3V. It sounded sickly when it was running on the single battery, so I went with the voltage regulator and two batteries to keep the voltage at 3V, instead of the slowing draining battery voltage. I'm wondering if just getting a higher dB rated buzzer will do the trick.

 

[Mister B]

Can you check the voltage across the buzzer? Maybe it isn't getting what it needs? Do you have the buzzer in the right way? I know it sounds silly, but I have overlooked something like that before. My buzzer will only make a weak sound if plugged in backwards.

 

[kim27]

I've double checked the wiring, rewired, altered the orientation, but alas, still somewhat quiet. I am wondering if the humidity is causing me problems.

The most likely culprit is my clock. Right now I'm running the clock off of the VLO, which is stated to be "around" 12Khz. Of course the spec says that the minimum it could be is 4 Khz and the max is 20 Khz. Either way, that will mess up my 4 Khz tone. I think I need to go about adding the crystal in so I have something more reliable and supports the low power modes.

Thanks for the thoughts, as looking at the data sheet reminded me about the 4 Khz tone needing a better clock.

 

[kim27]

I've set the buzzer to run off both a crystal and the DCO 1Mhz factory calibrated clock, and the buzzer doesn't get any louder. It looks like to achieve the desired dB I'll have to get a different buzzer.

 

[kim27]

I found the problem. I was using the wrong register to generate the PWM output. The audio better now.

 

[kim27]

You can find the latest code for my project at https://github.com/reflectivedevelopment/eggtemp

I built it using the latest Ubuntu with msp430-gcc.

Here is the data with an extra 12 hours of the last incubation cycle. Only one egg hatched!



Here is the temperature logger and buzzer in the incubator. At this point I still had not worked out the buzzer quirks. I'm also using the voltage regulator, which may not be necessary.



Here is an up close with the voltage regulator and the buzzer wired as suggested by the data sheet.



Here is what I think I will wire up into a more permanent model. I've added a crystal and removed the voltage regulator. I've kept a capacitor on that should help reduce noise on the ADC line to get better temperature readings; however, with oversampling this may actually hurt the sensitivity, so we will see.



We will be getting eggs in the next week or two, so I'll post status updates through incubation.

 

[Mister B]

Since you put the crystal in, does the buzzer work better?

 

[kim27]

Since you put the crystal in, does the buzzer work better?

The crystal does have the best tone, but the source of the problem was me using the wrong timer register. I'm surprised I got any tones out at all with the way I was doing things.

I think as far as reliability, it goes as follows.

1. Crystal is most reliable
2. 1MHz DCO (Digitally Controlled Oscillator) factory calibrated
3. 12 Khz VLO (Very Low Oscillator) which could vary from 4Khz to 20 Khz