Continually jumping off cliffs…

A friend of mine tweeted today:
“We have to continually be jumping off cliffs and developing our wings on the way down.” - Kurt Vonnegut
Since Friday (July 5th) I’ve jumped off of a lot of cliffs. About 9/10 times my “wings” didn’t work, leaving me to ask why. Okay, enough with the metaphors. On to ramblings about solder reflow and where my prototype boards are.

Wake up nRF51, wake up! You have Math to do!

Ah ha! I found it! How to have the nRF51422 wake up on sensing the ADS1247 is ready to be read. Unlike the ADS8321 I previously used which converts as it reads out, the ADS1247 takes a little while to do a conversion (depending on the rate it is set to), and as such the nRF51422 can take a nap most of the time. Otherwise it’s just burning through electrons pointlessly.

In the included libraries it defines the pins generically… but without interrupt, however in the powermeter example it defines the buttons manually in another library… with interrupts.

Below is an excerpt for button press with interrupt:

GPIO_PIN_CNF_SENSE_Low     << GPIO_PIN_CNF_SENSE_Pos

Below is an excerpt for a generic GPIO without interrupt:

GPIO_PIN_CNF_SENSE_Disabled << GPIO_PIN_CNF_SENSE_Pos

Some additional coding and configuration should allow me to sense the gpio pin that the DRDY line from the ADS1247 is connected to. When the line goes low the data is ready, and the nRF51 can wake up do a read, store the data, and sent it back to me via UART on the SEGGER J-Link. Later it’ll store the data for averaging later. This is the last major breakthrough I needed to figure out how to keep the nRF51422 in sleepy-time mode (Without using the above pictured Tea).

Onto gyro evaluation next. I just got confirmation my order shipped. My order from Adafruit on the thermocouple and thermocouple IC shipped. I haven’t heard about my solidstate relay though.

(Needed some other supplies too!)

Beta Testers Wanted –(KW/Waterloo/Cambridge/Toronto, Ontario)

I have to thank Ray from www.dcrainmaker.com for his post. I think it paints a pretty good picture of things. His posting did highlight something. My initial reluctance to BTLE. This stems from a personal experience choice, but mainly cost. However, if down the road I can get some form of backing and some help with coding I will be dropping in the nRF51922 microcontroller (ANT+/BTLE simultaneously) when released for dual support of both protocols.

One point he made was about getting a product to 95%. I think it’s being misunderstood that the accuracy of my meter is +/-5%. This is NOT the case. My torque testing is easily measuring in the 2% described by other’s products. I believe he means in terms of finishing. That’s a big hurdle. Redesign – Packaging – Waterproofing – Validation – FCC / CE approvals - ANT+/BTLE approvals. That’s the last 5% of developing a product and it’s a big 5%.

I’ve been having good progress with the nRF51422 (ANT+) microcontroller and I’m about 99.9% settled on the ADS1247/8. The ADS1247 is a 2 differential (4 single sided) ADC while the 1248 is 4 differential (8 single sided). Why I might chose the ADS1248 is so that I can have a secondary force sensing arrangement. That means I could do the fancy directional force output that Pioneer has shown off. It’s information overload during riding, but it might be useful. I think I’m going to try and design the board to accept both. Future proofing I’ll call it.

I’m glad a couple of people commented on the gyro situation. 4ma doesn’t sound like a lot, neither does 2ma, but when your coin cell’s life curve shows a maxim total draw for 2ma then that is a problem. I have a gyro I like being put on a breakout board by Protoadvantage now. I’m hoping to have it next week. I like coin cells, but the gyro could kill that… or sticking with coin cells could kill the gyro. If you have an opinion, post in the comments or drop me a line.

Now the other thing which this post is titled. Beta Testers. If you are in any of the above listed area’s, an avid cyclist, and interested in access to some beta prototypes drop me a line at kwakeham@gmail.com or kwakeham@accuity.ca. I’m looking for local first so I can drive over and debug / check / upload new firmware / get your feedback.

I’m looking at two months to get the new design in order and a prototype built. After that I suspect it’d be another month or two before I’ll put a meter in anyone's hands. However, if you are further away and interested drop me a line too. I’ve had several people ask. There is a list being compiled. When www.accuity.ca goes live there will be a sign up section. This will be a closed Beta, more like an Alpha test really. Generally that means I’ll own the device, you have a loan of it and I will eventually take it back.

Thanks for following! And Thanks to Ray again for supporting the industry.

More Testing V3 Power Meter and ADS1247

Some longer testing (1.5 hours) today and I’ve come to a few conclusions.

1. My calibration is off
2. It doesn’t matter that my calibration is off, the crank shear gauge on the inside of the driven arm to measure torque can be skewed by adding a twisting moment to your ankle.
3. As a result my power balance and power numbers are all wrong! And WAY off from the method of calculating averaged (non-accelerating) power for my Kurt Kinetic Road Trainer.

So I will be adding new strain gauges to V3 on the top and bottom of the crank arm. The arrangement removes bending so it will stabilize and remove this issue. I had said previously that it is the superior arrangement. I didn’t want to have to use two different types of gauges but my hand has been forced. However this raises the question about Stages power meter. What is their arrangement? I suspect it is not a shear arrangement, but rather a double bending arrangement but still on the back side of the crank. It’d lose sensitivity but gains in accuracy.

The ADS1247 is reading out. It’s looking noiser than I want, but this might be a function of my protoboard / power supply / poor wiring / random resistors used as a voltage divider. I still can’t find a potentiometer around my apartment anywhere even though I bought and wired one up specifically for testing months ago. I’ll make a trip to the dollar store tomorrow and hope

Snow Storms, ADS1247, .NETMF, and Friday Night

Snow day today which means I didn’t make it into work. Seriously though, I tried. Shovelling out at 8am when the snow was at it’s worse and not a plow in sight. Heard it was going to abate by 10am so figured I’d try again then. Everything I had shovelled looked filled in, waited until 12pm. It stopped, so shovelled again. Test run to Tim Horton’s made me realize it’s a death trap out there. Nothing that my Subaru Impreza with some Falken Eurowinter’s couldn’t handle, in fact I enjoyed it (once I turned OFF traction control). No, the problem is that people in Ontario tend not to buy winter tires, park on the street when they have a perfectly good driveway (filled with snow?), and generally do not know how to drive. In Newfoundland things would have likely remained opened and I would have gotten a coffee downtown with friends in that weather. In Ontario, 200+ accidents, not a plow in sight because they “wait” until it’s over. My street isn’t cleared and more poorly parked cars are now making it improbable to get down the road.

ADS1248 / ADS 1247 Received and Mounted

I got my breakout boards today for the 24 bit Sigma-Delta ADC’s. Soldered and conductivity tested. Now to wire them to an Arduino and a strain gauge. Approximately 3ma for the ADS1247, 2.048 reference means 5.85ma to each 350 ohm strain gauge setup. Still a little high, but we’ll see. Proto-Advantage was super quick in sending with regular snail mail. I live close to them (Hamilton, ON I think) so it’s not surprising.

ADS1247 / ADS1248

Well now that V3 is complete I’ve turned to debating what to do. I placed up my BT to ANT+ adapter, though few seem to have interest in that, or perhaps it was all the Hackaday traffic overshadowing everything on my V3 How To.

I mentioned that I might be looking to reduce complexity of the analog side and switch to a Sigma-Delta instead of an SAR. They are slower for the same amount of power but higher accuracy and less noise.

Well the 1247 (two differential input) and the 1248 (4 differential input) have been ordered as well as DIP Breakouts for the TSSOP-20 and TSSOP-28 from Proto-Advantage. I’m not in a rush currently as I have some major decisions to make in terms of continuing the power meter project.

That being said, Josh at Josh.to, has some ADS1247 code that he’s using to build an espresso machine. Like myself just over a year ago, he’s currently swamped in grad school. The code he’s developed in that time will certainly speed up my execution of the use of the ADS1247.

One thing Josh mentioned to me was that in order to switch inputs I would have to send a reconfiguration command. I infer I’d have to do a single read and then switch back and do another single read. While it would max out at 2000sps over 2 inputs, I’m sure the overhead in telling it to switch inputs would reduce that down.

An alternative would be to have an ADS1247 do one strain gauge and possibly a temperature sensor, and an ADS1246 single differential input do the other strain gauge but use the Vref from the ADS1247. These chips are about 12 dollars each, but compared to the 18 for the ADS8321 and the supporting electronics it still ends up being cheaper and simpler.

V4 would likely be coupled to an nRF51422 and again attempt for coin cell operation. This would be a copy of the reference design.

Some more notes on ADC’s

I haven’t had much luck getting the SAR’s to work as I’d like. Honestly, it’d work better in Rotor’s or Garmin’s arrangement, that is, if you are essentially running two independent power meters and one just transmits its findings to the master. That way it would effectively double my sampling rate. However, as it stands, I can’t process the data on the Arduino fast enough to average out the signals to reduce the noise enough. I’ve thought about bumping to 16 Mhz. Several people have done this, and so long as you maintain good voltage it should be fine, however it is officially below the minimum requirement of the Atmega328 or Atmega32u4 chips requirements for 16Mhz.