Start Your Engines....

In the ongoing process of making way too much work for myself reinventing my unfinished pit, I decided that my previous magneto switch was not acceptable. I bid and won a cheap bendix switch on ebay. I thought to myself "Hey Self! You are getting good at figuring out how to interface stuff! This will be easy to add! Probably plug it right in and it will work"!

WRONG!

The real magneto switch has some problems wit interfacing directly to my Bodnar card, because each switch position does not necessarily ground just one contact. It has a jumble of 8 contacts that have cryptic markings, and caused me a big headache with the multimeter to figure out the matrix. Once I did, I spent a lot of time scratching my head trying to figure out how to translate them into the 5 discrete switch outputs I needed. Decided to start from scratch, and just figured out how to do it!

Here is a picture of the switch back that has all of the contacts. Note that my thumb is covering up the contacts I did not need to use.

These contacts are labelled cw from center as follows:

cntr-grd

10 oclock-S

11 oclock-Bat

12 o'clock-New contact

1 o'clock-grd*

2 oclock-R*

*1 and 2 o'clock are connected by a small plate, screwed onto both contacts. Remove this plate to break the contact into 2.

Here is a view of the other side of the contact plate. It shows 2 modifications. The first is drilling a hole at the 12 o'clock position, and countersinking it to accept a 6-32 x 3/4 SS machine screw. This is screwed through the contact plate from the inside and secured with a nut on the other side of the plate. The second is the washer that is affixed to the center. This washer makes the center ground run all the way around the contact plate, instead of the eccentric shaped ground the original came with.

The final step is to modify the wiper for the switch. The wiper is a plastic wheel cut to fit three wedge shaped metal contacts. The meatal wedges are spring loaded to press up against the contact plate, and short the contacts to ground. The wedge has three dimples that are raised above the wedge at each corner. I removed one of the dimples by drilling it out, and dremelling it flat, so that the wiper only grounds one of the contacts, and not two. Then I placed a piece of electrical tape over the removed section of the wedge, so that it would not accidentally ground the contacts:



The above picture shows a combination of the original setup and the modified wedge. Remove the wedge contacts that are at the one o'clock and 6 o'clock positions. They are not needed. This picture shows the three dimples, how I removed the upper right one, and insulated the unneeded portion. The final wiper looks like this:


Reassemble the switch with the 2 screws, hook the outside contacts up to your favorite i/o card input and the center contact to ground on the card. Assign the button presses in FSUIPC and you are done!

Took me a lot longer to type this up than to actually do the mod. Hope it helps someone else.