Monday, May 3, 2010

Modifing for GSC™ 10 Cadence/Speed sensor for your trike

So you ride a recumbent trike or recumbent bike and all ways want a Garmin Edge 705 or the new Edge 500 but since the GSC™ 10 cadence/speed bike sensor that these GPS cycling computer work with will not work on anything except a diamond frame bike by design you have never gotten one. You could just use the cadence side of the sensor and let the GPS compute your speed and I did that for a while but I preferred the more accurate physical sensor. According to all the Garmin information one can purchase third party ANT+ speed sensors and use them with the Edge 705 or 500(I do not own a 705 just the 500). The manual say to go to a web-page '' for compatible sensors however there are no compatible sensors on that web-page, this is because there is not list of any kind on that web-page nor does anything come up when one searches their website. I bought two different speed only ANT+ sensors and tried to get them to work with the Edge 500 but it would not see either one and they both do work with a VDO Z3 I own that is also ANT+ compatible. I called Garmin and asked how can I get the Edge 500 to work with third party speed sensors or if I had the wrong one where is the list of the compatible one. The 'technician' I got on the phone did not seem to have any idea what I was talking about, five times he put me on hold and when to talk to a higher level person. Eventually he told me they would have to research this and get back to me. That was two weeks ago and in spite of additional calls I am still waiting. If their units do not work with ANT+ sensors they should just say so.
Well having a background in electronics I decided to trying to modify a Gamin GSC™ 10 cadence/speed bike sensor to allow it to both do cadence and speed. I am sure this WILL VOID any warranty on the GSC™ 10 cadence/speed bike sensor but I cannot see how it would have any effect on the warranty on the Edge 500 or 705.

First remove the Battery!
Next remove the rubber pad meant to go between the sensor and the bike frame, save this you will need to put it back on.
Remove the speed sensor arm by removing the screw, be careful the wired connecting the sensor are short and pretty fine - do not break them.
Then using a knife I separated the two halves of the unit.

Like this.

You can now easily see the brown and gray wire that connect the speed sensor to the circuit board of the unit. The wires do not penetrate the board and are just soldered to pads on the surface of the board. Be very careful desoldering these two wires if you pull up the pads you will destroy the circuit board.

Now desolder the speed sensors wires from the pads on the circuit board like this then pull the wires out.

Now you must know where the cadence sensor must be placed to allow the crank arm to swing past it with a magnet on it. From there you must measure to where you plan to locate the speed sensor. I have no way of knowing how long the wire in between the circuit board and sensor might be and still work but I would make it as short as is reasonable. I choose to put mine on the right front wheel using the the mount arm for the disc brake to hold it's mount. This you will have to work out for yourself, mine is mounted temporally on top of the VDO ANT+ speed sensor. When I get it mounted properly I will include a picture. Makes sure the wire is long enough but not a lot longer than you need. I would use either shielded wire or a twisted pair to reduce crosstalk in the wire and use a pretty small wire.
Now feed the wire through the hole where they came out or the screw hole. Then VERY carefully soldier the wires to the pads. Remember do not put any unnecessary stress on those pads.

Below you can see the wires soldered in and the wire pack in to the case. Remember there has to be space for the battery case and the wires will not fit between the circuit board and battery case. Be careful of putting stress on the pads when packing the wire in the case.

Below you can see the case reassembled. The case was originally sealed and held together with a silicone sealant. You MUST reseal the case. You will need to remove all the old sealant from both halves of the case and reapply a sealant to reseal the case, also the whole where the screw was and where the wire came through must be sealed especially around the new wire. I would wait to do this until you have tested both sensors but it must be sealed before it is used around any water. You must also let the sealant cure before attaching it to your trike because the zip ties used to hold it to the trike frame tend to make the case split open if the sealant has not cured.

Below you can see the other end of the wires tinned with heat shrinkable tubing already on them ready to solder to the leads coming from the speed sensor. I am not sure if it is important and most likely it would not matter but I made sure I attached the same wires on the sensor to the same pad as they came off of.

Below shows the speed sensor with the wires soldered together, the hear shrinkable tubing shrank and a wire tie attached to provide strain relief to the delicate wires that are original to the sensor.

It is not shown it the picture above but you should use the same silicone sealant to seal the speed sensor before exposing it to water.

I have had this installed and working for about a week now and have had not problems.

I did this to a spare GSC™ 10 Cadence/Speed sensor that I had bought thinking I could just use two - one for speed and one for cadence but Garmin would not let you do that either.

If you have a question publish a comment or send me a message on the forum or message board.


Warren Bowman said...

This is brilliant! Thank you so much for doing this. Do you have any pics of it mounted on the trike?

Ashby said...

Glad you liked it Warren - I thought it might help some folks but you are the only one who seems interested - I will update the photos with the unit mounted on my Tour soon. said...

Thanks for the tips on adapting the 705 for the trike. I just bought a used tour and will use your methods to adapt a 705 for my trike. Thanks also for the inspiration to get fit. I am a 67 YO who plans to lose 50 # over the next year or so.
George Cairns

Rainer Just said...

Thank You for the instructions. I have a problem with an e bike. My question: Is the speed sensor a simple magnetic switch? If it is so, You can just Buy one and mount it

Anonymous said...

I just modified my GSC 10 so that I could use it on a recumbent bicycle. Thanks for the instructions. I would not have tried if I had not seen that someone else had done so.

dna9 said...

Hi Ashby. I am a paraplegic who has just started to handcycle. I am planning to buy a Garmin Edge 500 to get speed, casence and heart rate data. How is your modification of the GSC10 holding out? As my cranks are no where near my front wheel I too would have to modify the GSC 10.

Ashby said...

dna9 - I no longer ride the Tour but now own two Catrike Expeditions and I have it installed on both of them working perfectly.

James McGowan said...

Thanks for this post. I was wanting to do this on my Catrike Expedition. I'll have to give it a try.

Thomas Nielsen said...

Just put 1 meter shielded cable on mine and it works like a charm. An easy operation, really, but a tremendous comfort to have seen the pictures first :-). Thanks.

- Thomas Nielsen

Thomas Nielsen said...

In an attempt to waterproof the speed sensor, I was a bit overenthusiastic with a heatgun when shrinking and accidentally damaged the insulation on the sensor leads. Instead of trying to open the sensor, I cannibalised an old Cateye wired sensor (because it is small and has strip-mounts) and voila! - it worked. So, in other words, the sensor *is* indeed a simple reed element. This time I was a bit more accurate with the heat gun.