digital thermometer help

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steveahart 20 years ago

Here's what I'm looking to build.......hopefully someone has some good advice or maybe even has already built something similar.

I've build circuits to detect temperatures in the past but I'd like to take it to the next level. I want to build a small, inexpensive circuit that will detect ambient air temperature changes, display temps to a small digital display, and even better, somehow log temp data (per second or so). My initial thoughts are to use a usb flash drive since they are small, inexpensive, and easily used with a desktop PC for later analysis of the temp data. Basically I want to place the thermometer at a location, leave, have the temp data logged, and be able to later review the temp data on a computer.

Anyone have any advice on this one?

Thanks!!!

Steve

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Spehro Pefhany 20 years ago

You'll need a fairly powerful (micro)computer to talk directly to a USB peripheral. You might do better with a CF or SD card.

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Ian Stirling 20 years ago

Define small, define inexpensive, and how long do you want it to log for?

As a quick hack, I'd be looking at a MP3 player, with external RAM.

Encode the sound in some form that the MP3 player can read.

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Tim Wescott 20 years ago

Or include some flash in the thermometer and make _it_ a USB peripheral. USB masters are hard to make, but slaves are fairly easy if you don't try to cross every 't' and dot every 'i' in the plug & pray mechanism.

Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/

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Ian Stirling 20 years ago

Or if you just pretend to be a serial/parallel port, and use one of the canned chips, which present an 8 bit 'friendly' bus.

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steveahart 20 years ago

My definition of small would be handheld size. Inexpensive is because I'll want to make like 5 of these, and hopefully it could log data for

2 hours or so, 1 hour minimum. I'm sure there's a way to make an electronic thermometer (I remember doing it in electronics class) but getting it to work with some sort of data logger is my big problem. I guess I'd like to see any circuit diagrams others might have come up with if they are willing to share.

Thanks

Steve

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Martin Riddle 20 years ago

Omega has data loggers just as you describe. I believe under $100.

Cheers

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Martin Riddle 20 years ago

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artie 20 years ago

Take a look at

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Hobo data loggers. USB or serial.

Namaste--

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xray 20 years ago

From the web page... GENERAL SPECIFICATIONS Measurement Capacity: 7943 readings

I wonder how that number came to be? 1f07 in hex doesn't help my understanding.

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Ian Stirling 20 years ago

Ok. What I would do, if I wanted to put one together quickly. As it's only 2 hours, the storage problem is simplified. Go to ftdichip.com, and find the link to the parallel 8 bit bus output ones. Now, two ways. A) Take a small PIC, and a temperature measurement chip - maybe one of the 'one wire bus' ones from TI, maybe not. Add an I2C LCD if you want, and a I2C eeprom chip. Accumulate samples at the specified rate until you can squirt them out the PC connected bus on demand. B) Take a 16 bit counter, a oscillator to clock data into the RAM, a

32K*8 SRAM (62256), an 8 bit ADC, a suitable temperature probe (lm10?), and again hook it to the ftdi chip, with some glue logic. When you turn on the 'log' switch, it clocks the counter, samples the temperature, and writes to the RAM. When you plug it in, it resets the counter, and reads from the RAM on demand from the USB port. You add another gate or two, and it writes to the USB port too, enabling you to wipe the memory to 0.

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William at MyBlueRoom 20 years ago

My Cricket Thermostat could be modifed as a logger. Just use the I2C temperature sensor and add an 24LC256 eeprom.

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Bill

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William at MyBlueRoom 20 years ago

My Cricket Thermostat could be modifed as a logger. Just use the I2C temperature sensor and add an 24LC256 eeprom.

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Bill

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William at MyBlueRoom 20 years ago

My Cricket Thermostat could be modifed as a logger. Just use the I2C temperature sensor and add an 24LC256 eeprom.

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Bill

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Spehro Pefhany 20 years ago

Probably 8K less some overhead for calibration parameters etc.

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GregS 20 years ago

My Fluke 189 has a variable width storage all depending on rate of change.

greg

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Michael 20 years ago

Take a look at:

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Its a PIC (sorta) tutorial and a temperature-logging project I found some time ago. Project uses a PIC16F84, 24C65 8-pin serial EEPROMs, and a DalSemi 1-wire temperature sensor. This project inspired the design of my own temperature logger. (I used PIC16F628 and 8 ea. 24LC256 EEPROMS though.)

IIRC, your temperature sampling is to be 1/sec. That might be too frequent to implement with a 1-wire sensor, taking its conversion time, all software overhead, and EEPROM write time into account. The DS1822, for example, takes

750 ms (max.) to do a conversion. My logger samples only once every 5 minutes, so I didn't have to consider conversion time, software overhead, or EEPROM write time in my design.

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William at MyBlueRoom 20 years ago

Since you're using I2C eeproms it might be more efficent to use an I2C temperature sensor and larger EEPROMs 24lc1024. Only 2 I/O pins too.

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William at MyBlueRoom 20 years ago

Since you're using I2C eeproms it might be more efficent to use an I2C temperature sensor and larger EEPROMs 24lc1024. Only 2 I/O pins too.

See my PIC projects at

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digital thermometer help

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