[Spridgets] Sigma 1200 Computer

[James Gruber]

I was able to get a Sigma Computer a few weeks ago from Nashbar complete with a Wireless Kit that I threw away, Something like $19.95 or $24.95. Range on the Wireless is limited to according to the Manual to 24 ". Like David I got a hobby magnet and used JB Weld on the brake drum. I fabricated a bracket from a piece of drapery rod hardware and an L bracket and bolted it to one of the bolts on the Leaf Spring Bracket. I used phone wire and soldered to the sensor / magnetic reed switch to extend the wire through the tranny tunnel and come out the hole on top of dash, where the Left Tonneau snap is next to the Rear View Mirror. I used a L shaped bracket to attach to one of the mounting holes to the bracket for the rear view mirror. 
   
  Display is in easy visual sight without having to look for it. With polarized sunglasses on difficult to read display in bright sunlight. Other than that, very accurate speed wise,. I zero'd the odometer reading and elapsed distance on the Sigma 1200 and after a full tank of gas they were within a 1/4 mile of one another.
   
  I did set up a quick disconnect under the dash using a simple telephone set line cord female to female cable extender adapter. That way I could test the sensor unit at the rear wheels to see how close or far away I could place the magnet. I checked for continuity with my VOM as I rotated the wheel. Once I know I could get a repeatable signal from the sensor I then moved to mounting the display on the dash. Move the magnet as far away as you can and still have it open and close the reed switch.  Works real slick and since my analog speedo was bouncing all over the place and was the wrong gearing this solved a problem. A fun engineering project.
   
  Since then I think I've managed to break a wire going to the display and have not had time to loook at it. I'll be happy to send pics if anyone is interested of how I mounted the senson and the display. 




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Message: 6
Date: Fri, 20 Jul 2007 20:29:02 -0500
From: "David Lieb" 
Subject: Re: [Spridgets] New Smiths 130 MPH 3.5" Speedo, $50
To: "Bill L" 
, "Spridgets"

Message-ID: <03f301c7cb36$86912480$0401a8c0 at midget>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original

> i see some of the sigma bicycle computers are even wireless!!!! 
> which
> model(s) do you use/recommend?..

I use the BC1200, but I believe it has been discontinued. I do not recommend 
the wireless, since there is a significant amount of groundplane between 
source and reader. I tried several different mountings to read the wheel 
rpm. First attempt was inside the brake drum, but it did not account for the 
amount of lateral motion of the hub and did not read consistently in corners 
and curves. The second attempt went to reading the driveshaft rotation at 
the diff. Nice consistent readings, but the pulses per second were too high 
for the computed functions... speed readout was perfect, but odo readings 
did not increment properly when you were over 60mph or so. When a 750 mile 
drive registerd as 400 miles, I figured I ought to correct something. 
Fortunately, the trip gave me plenty of time to figure out what might be 
causing it... I ended up using JB Weld to attach the magnet to the rear 
brake drum and mounting the reed switch on a metal strap attached to the 
backing plate. Works good.
I am told that dollhouse wiring works well for extending the distance.
David Lieb 




Jim Gruber
Bugsy '68 Sprite (future Bugeye in disguise)
Cincinnati, OH
       
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