The Digital Temperature Logger is a simple temperature data logger that records temperature at periodic intervals and operates over a wide temperature range. It is based on the Microchip PIC12F683 microcontroller and can log temperature for up to 5 days (126 hours).
This kit offers easy assembly and simple operation. Data is stored in non-volatile memory for later download to a computer. The DTL plugs directly into a standard DB9 RS-232 serial port or a DB9 serial cable (available below) allowing data to be transferred to a computer using a terminal program such as HyperTerminal.
See below for selected temperature data logging applications.
Frequently asked questions.
Parts included with the kit. (Click for larger view)
Standard RS-232 DB9 serial cable.
Temperature Data Logger Applications
Measure the temperature coefficient of a component.
The digital temperature logger was used to record ambient temperature for 24 hours while the voltage of a 10V reference was monitored.
An Agilent 34410A multimeter was used to log the reference voltage.
The temperature coefficient of the AD587LN precision voltage reference is found by plotting the reference voltage (in ppm relative to the average value) versus ambient temperature. This particular part has a measured temperature coefficient of -1.35 ppm/C.
Monitor the weather.
Two digital temperature loggers were placed outside for 4 days and the results are shown below. The measurements from both units are in good agreement.
Monitor freezer performance.
The temperature log from inside a freezer is shown below.
After the logger reaches thermal equilibrium, a series of temperature cycles can be seen. The temperature inside the freezer rises when the compressor is off and falls when the compressor is on. The spike at around 135 minutes corresponds to the freezer door being opened briefly. During steady-state operation, the freezer temperature stays between -1F and +7F, within range of the guidelines for effective food storage established by the
USDA.
Frequently Asked Questions
Q. What if my computer doesn't have an RS-232 serial port?
A. See answer to next question.
Q. Can a USB to serial cable be used with the DTL?
A. Yes. The DTL has been tested with the
USB-RS232 Cable (UC2321-AKE) available from Saelig for less than $12.
Q. Are there any alternatives to using HyperTerminal to transfer the data?
A. Yes. A very nice terminal program called Developer Terminal is available from
Smiley Micros and it is free. :) See the Downloads section on the lower left side of the Smiley Micros home page.
Q. Is there an Excel template file available for plotting the data?
A. Yes. Click here to download the Excel template.
Q. What are the sample interval options for logging data and how are they selected?
A. Four logging intervals can be selected: 1 min, 6 min, 15 min and 30 min. These are selected by setting two slide switches.
Q. What is the typical battery life?
A. The DTL uses 150uA (average) when it is on and logging. The CR2032 battery gives about 220 mAh at 25°C. This would give about 1450 hours (60 days) of battery life. Battery capacity is reduced by about 5% at -10°C. I have seen 3-packs of CR2032 lithium 3V batteries for $1 at various dollar stores.
Q. Can the data logger be configured to measure voltage instead of temperature?
A. Yes. This would require changing the microcontroller firmware. Contact
Micro Circuit Labs for details.
Q. What parts are included with DTL kit?
A. The DTL kit comes with a complete set of parts, shown below. See the manual for more details.
Parts List:
Reference Qty Description
Battery 1 Battery, 3V lithium coin cell battery, CR2032
BT1 1 Coin cell battery holder
C1, C2 2 Cap, 0.1uF, ceramic (marked “104”)
D1 1 Red LED
D2, D3 2 Diode, small signal, 1N4148
J1 1 Connector, DB9 female, PCB mount
Q1 1 NPN transistor, 2N3904
Q2 1 PNP transistor, 2N3906
R1, R5, R6, R7 4 Res, 10K, 5%, 1/4W (brown-black-orange)
R2, R8 2 Res, 4.7K, 5%, 1/4W (yellow-purple-red)
R3 1 Res, 10K, 1%, 1/4W (brown-black-black-red)
R4 1 Thermistor, 10K, NTC, Thermometrics #RL0503-5820-97-MS
SW1, SW3, SW4 3 Switch, mini-slide, SPDT
SW2 1 Switch, push button, momentary on
U1 1 Microcontroller, Microchip, PIC12F683-I/P, pre-programmed
Misc. 1 8 pin socket for U1
Misc. 1 DTL printed circuit board (1.5” × 2.5”)
Q. What type of enclosure do you recommend?
A. I recommend an ABS utility box, part number ACS1534 available from www.bgmicro.com for $3.59. The DTL can be mounted to the cover so that the DB9 connector and switches can be accessed when the cover is removed.
For test purposes, I have been using the following: cover the solder side of the board with a strip of duct tape, enclose the digital temperature logger in a small zip lock bag. Several of these bags are included with the kit. This is not the most rugged but it has been adequate and is waterproof.
Q. What if my question isn't answered here?
A. Contact us and we will do our best to provide an answer.
Contact Micro Circuit Labs.
