Another kind of relay driver board used to utilize your old PC

Posted on Feb 5, 2014

This article means to utilize your old PC to be come a simple controller. Many old PC like 8088 type, 8086, 80286, 80386, or even 80486 already become an obsolete systems, since they can not run many new program now a days. In fact, this system still also can be run well. Many people has let their own not used, since they have a new one (pentium t

Another kind of relay driver board used to utilize your old PC
Click here to download the full size of the above Circuit.

ype). Thus what for this old system now For people like us, we can use this old PC to make any experiment. Here I will stimulate you to take advantage, make a simple controller using 8 relays to make a variety uses like; turning on/off lights, turn your home stereo set, on/off you home appliance, make a timer device, make a home device alarm, etc. All application depends on your imagination. This board using 8-bits of LPT printer parallel data port (DP) to activate the relays. LPT printer parallel port also have 4-bits additional port (PC) which can be utilized too. But this is not implemented in this design, because in my opinion, 8-bits are more than enough, and beside that this size (1 byte) fit each of 8255 PPI port if we want to interface it too. The basic is the same for all the eight channels. To protect the LPT port from damage, I use optocoupler to isolated the PC side (+5V) and relay circuit (+24V). You can change the relay voltage type to +12V or even +6V if you can find one. This type of optocoupler, PC914 can be replaced with another type like 4N series (4N22 ~ 4N28, 4N35, 4N47 ~ 4N49, etc. ). Using a common driver combination, transistor Q1 ~ Q8 (hi-power) to drive the relays. D1 ~ D8 use to protect the transistor from any transient current when the relay is in the off state. The resistor values are chosen to make transistors get full enough saturated when it is on. This common driver also can be change using...

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