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Hi guys. Of course I realize this topic is not amp related, but I am having an electrical dilemma that would be more suited to a group of electronic guys than a group of motorcycle guys.
Problem is with my electronic speedometer, which is known to have a pretty high failure rate around this era (mid 90's). It is an analog sweeping pointer type display on a round dial. It is a simple hook up. It receives a switched +12v from the ignition. It uses this to power the speedo internally, as well as a couple of incandescent lamps. It also splits this 12v and ground to send out on a three wire harness (red, blk, white) to the Vehicle Speed Sensor mounted on top of the transmission. This powers a Hall Sensor square wave signal relative to the speed of the teeth of a gear in the tranny. This signal is then fed back to the speedo on a white wire, where the speedo uses it to drive the powered speedo dial motor and odometer. It also works with the directionals to self cancel.
My speedo acts a little nervously at times at idle with the bike not moving by twitching around a little between 0 - 4 mph Then after riding for perhaps 10 miles, the dial just drops dead to 0 mph, and the odometer stops counting. The directionals won't self cancel, but in this case that is to be expected. Vehicle speed seems not to be a factor, and as far as I can tell in the daylight, the 12v indicator bulbs stay lit. It aslo at this time seems to be heat related in that it usually works when setting out after sitting for a time, but at some point goes into failure yet once again.
I wanted to see what the 12v was doing when riding, so I wired up a bright LED/resistor to the red wire that goes down to the new speed sensor that I just replaced. In this case, when the speedo dumped to 0 mph, the led stayed lit, telling me I had good supply voltage. And since the sensor voltage is fed from and thru the speedo, I assume the speedo is staying powered as well.
Then I wanted more than what an LED could react to regarding voltage fluctuations, so I wired an analog panel mount dial gauge to that same red wire down under the seat going to the speed sensor. This allowed me to watch the speedo and the volt meter at the same time. But, when the speedo acted up, the volt meter did not. OK, good supply voltage.
So now I get to my trouble area, measuring the square wave return pulse from the speed sensor. I want to know the same thing about it, what is the signal fed back to the speedo doing when the speedo dial drops dead while riding? I can raise the rear wheel of the bike with my o-scope on the white signal wire while the bike is in the garage, and hand spin the rear wheel in 5th gear to observe what the signal looks like. But this doesn't really tell me much from a riding perspective. Since I can't ride around with an o-scope hanging off the bike, I need some other, (crude as it may be), way to observe the square wave when the dial drops to zero. So far, I have not come to a solution for this, and don't want to go out and buy a hand held wave analyzer for this one job.
So, who knows how to monitor this signal in a meaningful way on a motorcycle on the road in the sun? I know I could tie my Fluke to it, but this would give me only an ever changing numerical value, not really the visual I would like. I have ordered an Arduino based square wave generator to be able to feed the speedo from it to observe the dial, but again, it doesn't really tell me much regarding intermittant heat related failure on the road.
If all this leads me to concur the speedo is in fact faulty, I have at least some hope held out that maybe I could crack this speedo open (possible, but difficult) to see if I could find what it seems might be connection based. Of course this also risks totalling the speedo, which given how difficult and expensive it would be to replace with either another used one, or aftermarket take your chances roll of the dice replacement, seems worth a try.
I have included a basic drawing of the circuit.
Problem is with my electronic speedometer, which is known to have a pretty high failure rate around this era (mid 90's). It is an analog sweeping pointer type display on a round dial. It is a simple hook up. It receives a switched +12v from the ignition. It uses this to power the speedo internally, as well as a couple of incandescent lamps. It also splits this 12v and ground to send out on a three wire harness (red, blk, white) to the Vehicle Speed Sensor mounted on top of the transmission. This powers a Hall Sensor square wave signal relative to the speed of the teeth of a gear in the tranny. This signal is then fed back to the speedo on a white wire, where the speedo uses it to drive the powered speedo dial motor and odometer. It also works with the directionals to self cancel.
My speedo acts a little nervously at times at idle with the bike not moving by twitching around a little between 0 - 4 mph Then after riding for perhaps 10 miles, the dial just drops dead to 0 mph, and the odometer stops counting. The directionals won't self cancel, but in this case that is to be expected. Vehicle speed seems not to be a factor, and as far as I can tell in the daylight, the 12v indicator bulbs stay lit. It aslo at this time seems to be heat related in that it usually works when setting out after sitting for a time, but at some point goes into failure yet once again.
I wanted to see what the 12v was doing when riding, so I wired up a bright LED/resistor to the red wire that goes down to the new speed sensor that I just replaced. In this case, when the speedo dumped to 0 mph, the led stayed lit, telling me I had good supply voltage. And since the sensor voltage is fed from and thru the speedo, I assume the speedo is staying powered as well.
Then I wanted more than what an LED could react to regarding voltage fluctuations, so I wired an analog panel mount dial gauge to that same red wire down under the seat going to the speed sensor. This allowed me to watch the speedo and the volt meter at the same time. But, when the speedo acted up, the volt meter did not. OK, good supply voltage.
So now I get to my trouble area, measuring the square wave return pulse from the speed sensor. I want to know the same thing about it, what is the signal fed back to the speedo doing when the speedo dial drops dead while riding? I can raise the rear wheel of the bike with my o-scope on the white signal wire while the bike is in the garage, and hand spin the rear wheel in 5th gear to observe what the signal looks like. But this doesn't really tell me much from a riding perspective. Since I can't ride around with an o-scope hanging off the bike, I need some other, (crude as it may be), way to observe the square wave when the dial drops to zero. So far, I have not come to a solution for this, and don't want to go out and buy a hand held wave analyzer for this one job.
So, who knows how to monitor this signal in a meaningful way on a motorcycle on the road in the sun? I know I could tie my Fluke to it, but this would give me only an ever changing numerical value, not really the visual I would like. I have ordered an Arduino based square wave generator to be able to feed the speedo from it to observe the dial, but again, it doesn't really tell me much regarding intermittant heat related failure on the road.
If all this leads me to concur the speedo is in fact faulty, I have at least some hope held out that maybe I could crack this speedo open (possible, but difficult) to see if I could find what it seems might be connection based. Of course this also risks totalling the speedo, which given how difficult and expensive it would be to replace with either another used one, or aftermarket take your chances roll of the dice replacement, seems worth a try.
I have included a basic drawing of the circuit.
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