Summary of PC Temperature Meter using ATtiny15 microcontroller
This article describes a four-channel temperature meter adapter that operates without an external power supply, drawing 5mA from a PC's COM port. It utilizes an ATtiny15L microcontroller with an internal A-D converter and 103AT sensors to measure temperatures between -40°C and +105°C with ±0.5°C accuracy. The circuit requires no adjustment and is designed for easy construction and data logging via a PC.
Parts used in the Port-Powered Temperature Meter:
- ATtiny15L Micro-controller
- 103AT Sensor
- COM Port Interface
- AVR Programmer (HVS mode)
Port-Powered Temperature Meter
This is a four-channel temperature measurmet adapter that works without external power supply. It will suitable for measureing temperature and logging its data with a PC. The circuit diagram is very simple and no adjustment is required, everybody will able to build it with ease 🙂
| Micro-controller | ATtiny15L (Atmel) |
| Number of channels | Four channels |
| Measurement Range | -40°C to +105°C (0.1°C/step) or raw A-D value |
| Measurement Error | ±0.5°C (at room temperature) |
| Sensor | 103AT (Semitec) |
| Power Supply | Supplyed from COM port (typ. 5mA) |
| Cost | Approx. 1200JPY (All parts) |
HARDWARE
Micro-controller
I chose an Atmel ATtiny15L for this project. It is the only device that has a built-in 10bit A-D converter in the 8 pin AVRs. The A-D converter has a bandgap reference and differencial amplifire as its front-end. The AVR core is clocked by only internal RC oscillator (calibrated to 1.6MHz), any other clock souce cannot be used. Also 25.6MHz clock source that 16x multiplied from core clock is available for timer/counter. This means that a fast PWM output can be generated. Therefore the ATtiny15L has good analog I/O capabiltity.
In this project, the A-D converter is used as four channels, single-ended, no gain and VREF from Vcc configuration. However RSTDISBL fuse must be programmed in order to use pin #1 as one of the analog inputs, an AVR programmer that can program in HVS mode is required.
Power Supply
The devices that works on the COM port without external power supply, such as serial mouse, are powered from the COM port. When an application program opens COM port, ER and RS signals will go high. The high level voltage is from 6V to 12V at most PCs, and it can supply 5mA at least. This is sufficient for low power micro-controllers.
For more detail: PC Temperature Meter using ATtiny15 microcontroller
- How does the device receive power?
The device is powered directly from the COM port when an application opens it, utilizing ER and RS signals. - What is the measurement range of the meter?
The measurement range spans from -40°C to +105°C with a resolution of 0.1°C per step. - Can anyone build this circuit easily?
Yes, the circuit diagram is very simple and requires no adjustment for everyone to build. - Which micro-controller is used in this project?
An Atmel ATtiny15L is used because it features a built-in 10bit A-D converter in an 8-pin package. - What clock source drives the AVR core?
The AVR core is clocked by an internal RC oscillator calibrated to 1.6MHz. - Is external programming equipment required?
Yes, an AVR programmer capable of HVS mode is required to program the RSTDISBL fuse. - What is the typical current consumption?
The device typically consumes 5mA of power supplied from the COM port. - What is the estimated cost for all parts?
The approximate cost for all parts is 1200 JPY.
