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Pedal load sensor/ power meter for auto shifter.
#11
I have been working on a project lately for my job involving reading extremely accurate pressures out of a load cell that has a large span (300psi)

I was able to read pressure variations to around 0.003 psi. I could not use amplification because of noise issue and the output was max 100mV
To achieve such precision, I used an ADS1510 16 bit DAC coupled with an Arduino and some fancy software based filtering (it took an engineer and me two weeks to calculate those filters!)

Load cells are hard to work with because of their low output and bad signal to noise ratios...

Good work out there!
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Si ça a déjà été fait, je peux le faire
Si ça n'a jamais été fait, donnez-moi juste le temps de trouver comment !


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#12
That's an incredible level of accuracy. Even though you've got 50 times the voltage to work with its way above what I could achieve. Interesting that you've not used an amplifier. 
Will hire a pedal based power meter one day and check mine for accuracy.
- Oran
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#13
I’ve successfully put the NRF24L01 inside the power meters metal case. Wasn’t any bother to do, I just added an extension wire to the antenna of a length recommended by a website. Although other websites say this should not be done but so far its worked. Only half of the antenna extension is actually outside of the case which seems to be enough. These NRF24L01 modules have worked very well and I really like the instant connection compared to Bluetooth. 

[Image: uCG6ZW.jpg] [Image: mZTRuJ.jpg]
- Oran
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#14
I couldn’t hire a power meter but I’ve sort of borrowed one off Ebay. Well I’ve bought a second hand pair of Garmin Vector 2 pedals which I’ll sell on when finished with them. I got the dual sided version is I can find out what my left right balance is and exactly how much power my right leg is producing.

So the initial impression after 9 rides is quite unbelievable. My homemade power meter that cost me around £15 is consistently within 5 - 10 watts of an £800 power meter. I really couldn’t expect any better from a single sided power meter and its more than adequate for the auto shifter.

I would normally post a graph but the image hosting sites are now asking for money and not decided were to go next with that. Instead I’ve attached the entire spreadsheet so you can go through the data in more depth if you want.

What has become quite clear to me is that it’s the last few % of accuracy that costs so much. I’m excited now for the next version based around an nRF52832 Bluefruit feather. The specs for it seem too good to be true as its so much more than a wireless communication chip capable of ANT+ and BLE. It has a 12 bit ADC, 64Mhz 32bit processor, runs on single cell lipo with on board USB charging and low power consumption.

Ideally the auto shifter it’s self would pick up ANT+ signals from a power meter and maybe more. This way it could work with other bought power meters. Potentially it could work with an ANT+ speed and cadence sensor but don’t think it wouldn’t  be very responsive. I’ve got so much to learn about ANT+ and its protocols but I think it transmits once a second.

One day it may be possible to have the electronics, battery and servo in one box. The option of 3 inputs from reed switches, speed, cadence and derailleur or have some of these from ANT+ sensors.
- Oran
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#15
Realized the file hadn't attached due to the size 4.4MB. I'm experimenting with sharing files from Onedrive, link below. 

https://1drv.ms/x/s!ArnsxW04vTodkNE_mRqITFNm6E8_gg
- Oran
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