Jeremy Harris
100 MW
I know that having a Watts Up or Cycle Analyst bolted to the handlebars gives you loads of useful information, but most of the time I find I only want to know two things:
1. How much battery capacity do I have left?
2. How much current am I pulling?
For practical purposes you only really need to know either of these to about the same accuracy as the gauges in a car. Analogue meters are easier to read 'at a glance' than digital displays, but look clunky. You can get tiny LCD analogue meters though, that not only look neat but are also weatherproof.
As part of an update to my stealth folder (see the other thread in the ebike photos section) I decided to design, build and fit a simple fuel gauge. This is what it looks like on the handlebars:
![Gauge on handlebars.JPG Gauge on handlebars.JPG](https://endless-sphere.com/sphere/data/attachments/26/26738-3c4558b8e0e10424376039671bcacd7c.jpg)
The small switch changes the display from capacity remaining to instantaneous (well, the sum of 100 samples taken over a second) current. There's nothing in the little handlebar box except the meter and display, the stuff that drives it sits inside the controller case. The controller already has a shunt for measuring current, which is easy to tap into, so this is what I used. The controller circuit is a tiny module about 1.5" x 1", covered in heatshrink, that just stuffs inside the controller case. A thin four core cable runs up to the display on the handlebars. The module is powered by the 5V supply on the controller (it only draws a couple of mA or so). I've left the serial programming port in place (the three pin connector in the next photo) so that I can update the code if needed. Here's a picture of the finished microcontroller module:
![Microcontroller module.JPG Microcontroller module.JPG](https://endless-sphere.com/sphere/data/attachments/26/26739-34c25e9be4d45f90126375356624c6c4.jpg)
The way it works is to store the state of charge of the battery (in amp seconds) in non-volatile memory (so it remembers it when the power is off) and just subtract the Ah used as you draw current from the battery, by measuring the voltage across the controller shunt. There's a reset button on the controller that if pushed at power on resets the gauge to 'full'. The actual capacity is programmed in the code - mine is set for 10Ah. If the battery gets within 10% of being flat, then the display switches to overload mode and flashes all the pointer bars as a 'low fuel warning'. You can still switch to current mode to see how much you're drawing and eke out the last bit of capacity as a 'get you home' measure. It'd be best to always recharge before this point though and this gauge makes that pretty easy to work out.
If anyone wants it I can post the schematic and code. It's not hard to build and the code can be programmed into the chip using free software and the same 5V serial interface used to talk to the XieChang controllers.
Jeremy
1. How much battery capacity do I have left?
2. How much current am I pulling?
For practical purposes you only really need to know either of these to about the same accuracy as the gauges in a car. Analogue meters are easier to read 'at a glance' than digital displays, but look clunky. You can get tiny LCD analogue meters though, that not only look neat but are also weatherproof.
As part of an update to my stealth folder (see the other thread in the ebike photos section) I decided to design, build and fit a simple fuel gauge. This is what it looks like on the handlebars:
![Gauge on handlebars.JPG Gauge on handlebars.JPG](https://endless-sphere.com/sphere/data/attachments/26/26738-3c4558b8e0e10424376039671bcacd7c.jpg)
The small switch changes the display from capacity remaining to instantaneous (well, the sum of 100 samples taken over a second) current. There's nothing in the little handlebar box except the meter and display, the stuff that drives it sits inside the controller case. The controller already has a shunt for measuring current, which is easy to tap into, so this is what I used. The controller circuit is a tiny module about 1.5" x 1", covered in heatshrink, that just stuffs inside the controller case. A thin four core cable runs up to the display on the handlebars. The module is powered by the 5V supply on the controller (it only draws a couple of mA or so). I've left the serial programming port in place (the three pin connector in the next photo) so that I can update the code if needed. Here's a picture of the finished microcontroller module:
![Microcontroller module.JPG Microcontroller module.JPG](https://endless-sphere.com/sphere/data/attachments/26/26739-34c25e9be4d45f90126375356624c6c4.jpg)
The way it works is to store the state of charge of the battery (in amp seconds) in non-volatile memory (so it remembers it when the power is off) and just subtract the Ah used as you draw current from the battery, by measuring the voltage across the controller shunt. There's a reset button on the controller that if pushed at power on resets the gauge to 'full'. The actual capacity is programmed in the code - mine is set for 10Ah. If the battery gets within 10% of being flat, then the display switches to overload mode and flashes all the pointer bars as a 'low fuel warning'. You can still switch to current mode to see how much you're drawing and eke out the last bit of capacity as a 'get you home' measure. It'd be best to always recharge before this point though and this gauge makes that pretty easy to work out.
If anyone wants it I can post the schematic and code. It's not hard to build and the code can be programmed into the chip using free software and the same 5V serial interface used to talk to the XieChang controllers.
Jeremy