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Battery Powered Lecturn Lamp

The lecturn lamp was a project that I had been waiting to do for a while. Several years ago, a new lecturn was built to match the the rest of the chancel furniture. It even had a light that could be used in the evening. However, the light had to be plugged into the wall and running extension cords over the floor was a safety issue and the plug that was built-in kept getting pulled out of the lecturn base causing the wooden legs to come apart. So, I took it upon myself to hook up a battery operated light that would be just as effective, yet be self contained with no wires. I bought a "Littlite" 12 Volt light with a goose neck, and replaced the large, bulky 120 Volt lamp with the Littlite and a little modification. I built a charging circuit and battery holder from a bent piece of aluminum stock I had. This worked for one season, but since it was just thrown together, the battery and charger would bounce around inside the lecturn stand any time it was moved, and the heavy battery could come out and smash on the floor (or someone's foot). So I disconnected it and did not have any light on the lecturn for a few years.

During this time I was thinking of ways to charge the battery without anyone being responsible for the charger. I planned to use photo cells to charge the battery in the day and keep it topped off for the evening. In order to do this I would need to design a charging circuit and rebuild the top of the lecturn to fit in the photo cells. This was a great idea, but I did not have the time or resources to put this together. So nothing happened.

But, this year (2005) Lent has come early and church services are dark at 7:00 p.m., so I had renewed interest in getting the light working again for good. I took a few days and designed a new circuit that would not let the battery completely discharge itself, and would let you know when it needed to be charged, and in a pinch could be plugged in and used if the battery were dead and needed charging. The following is what I came up with to meet those goals, and in the future I can add a photo-voltaic charger if time allows.

The final, working circuit uses zener diodes to detect the lower voltage in the battery and then the warning circuit uses the same kind of detection, but has an extra MOSFET to invert and turn on the flashing LED indicating that the battery needs a re-charge.

After the circuit is designed and tested, the circuit can be transfered to trace artwork for etching the copper clad circuit card. This can be a long process of checking and double checking the traces. If not correct the circuit may not work.

The almost completed artwork. I use rub on traces to create the artwork on the copper. All the copper you want to save must be covered. There are many ways to transfer the artwork to the board, but for a one-off custom board, it is faster to just use the rub off traces.

The next step is to etch the copper off the board with ferric chloride. This took about 40 minutes. It takes less time if you heat and vibrate the board.

After the etching you must fully rinse off the board and remove the trace coverings. This is the cleaned card after the coverings were removed.

Next, I brushed the copper with steel wool and drilled some holes in the board for the component wires to go through.

Here is a better picture showing the paper through the holes. I want to drill all the holes on the large board before I cut it down so that it is easier to handle.

The component side if the board. Some holes are bigger for larger gauge wire.

I then cut the card down to size and tin the copper with solder. This protects the copper from oxidizing and makes installing the components fast. I first melt solder all over the board using a flux and then use a solder sucker or braided copper to absorb the excess.

The components are then mounted and the card is re-tested.

I bought a box at Radio Shack that could house the whole circuit and hold any battery acid if the battery should leak. The battery is a sealed lead-acid battery so it should last a while.

Here you can see the shutoff control circuit mounted above the level of any battery acid level.

The light dimmer control and low battery light will be the only visible part of the project. The light uses a BNC jack to interface with the top of the lecturn.

The completed project will be Velcro'd into the lecturn.

The lecturn without any light at all.

Velcro holds the box into place inside the lecturn.

The finished installation.

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