Friday, January 22, 2010

Miniature Real-time Controller based on microcontroller AT89C2051

This microcontroller project was design and implemented by Wichit Sirichote from thailand. the device that controls home's night light, air-conditioner,etc. The device is a Miniature Real-time Controller. The circuit uses only three chips, a 89C2051, DS275(or MAX232), and 74LS07 open collector driver. The scheduler for time on/off of 6-channel output can be made by downloading from PC and saved into onchip RAM. Each output provides a 20mA sinking suitable for driving a homemade opto-triac or big solid-state relay for heavy load.

A Microcontroller AT89C2051 with a low-cost X-tal 3.579MHz runs timer6.hex. The 6-channel output is P1.2 to P1.7 driving with sink current. A 74LS07 open collector provides approx. max 20mA @12V suitable for driving a homemade opto-triac shown in Figure 2. Two signal diodes, 1N914, provide simple backing up supply for the AT89C2051. Since RST uses simple RC circuit, there is no brownout protection and reset switch thus when the controller operated with battery for long time, the chip may knock. Simply take the battery out and put them again. The RS232 level converter, instead of DS275, any converter may use, or simple circuit using two transistors.

Link: source