Wednesday, November 5, 2008

Project: Ring Detector

This was the first project that I built from my own design for my own use.

Basically its a simple ring detector with a flashing LED and a reset button. It plugs into a basic analog telephone line. When it detects a ring voltage, it starts flashing the LED and keeps flashing it until it is reset by pushing the reset button.

I built this because, at the time, I had a basic analog phone at work with voice mail. I didn't get many voice mail messages, so when I didn't remember to check for messages. This was my solution. When I was away from my desk and the phone rang, the light would flash until I reset it. I would reset it after I checked my voice mail - problem solved.

Version 1
The first version was built in a basic project box with on a pad per hole PCB that was designed specifically for the project box. I purchased this one from Jameco as I did most of my parts back then.

As you can see from the image, I used basically a point to point construction technique on this version. Most of the connections were made using the extra leads from the components, which I soldered to the pads of the other component to which it was connected. I also used copper tape to make some of the connections. This process was fairly easy to do, but did require a bit of planning for the layout of the components. This is the only project I built with this technique, so clearly I did not find it too impressive.

The Top side of this board shows the basic component layout. The two white wires shown were cut from the momentary reset switch. The four pin header with one pin removed was for the power (battery for this model. The two pin header between the four pin header and the two electrolytic caps connects to the LED mounted in the case. The other two pin header on the top left connected to the phone line (RJ11 jack).

The complete unit fit into the project box with a 9V battery provide power. I used this unit successfully for months until the battery ran out and I decide to upgrade.

Version 2
PCB Board Layout

Final Schematic

Board Parts Layout

The final version was produced using the PCB layout available from the links above. I created this board using the toner transfer method with Press-n-Peel PCB Transfer film

Basically this stuff is a special blue polyester film that you print a PCB pattern on using a laser printer. Then using a household iron, you melt the toner off of the film onto your prepared copper clad board. Then you etch the board using a chemical process. I used Ferric Chloride from the PCB kit I purchased.

The process was pretty easy, and resulted in a pretty good board, but I really dislike chemical etching because the chemicals are pretty nasty to work with and dispose of. Others apparently like it as a process, and it is hard to argue with the ease of use or the quality of the results that can be achieved.

Credit for the ring detect circuit based on the 6N139 optocoupler and 2N3906 transistor goes to the now defunct Home Automator Magazine. The addition of the flashing LED and reset circuit are mine.

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