Packaging the Analogger
The Analogger is actually smaller than the large screen CA but is not sealed and has a switch, USB port, and removable micro-SD card slot. The Analogger manual
suggests tucking it away to protect it from the elements and also calls out the mechanical sensitivity of the SD card slot mechanism. Not too good for trail dust, rain, etc. There are no connectors or openings for the extra two analog channels, making using this a solder and drill DIY affair. There are two connectors: one for power and one for the serial data stream – the extra analog data requires a third connector. In short, the Analogger is ruggedly constructed but is a ‘Sunny Day’ design that needs a bit of DIY tinkering to be trail-ready. The manual calls all this out so no surprises or complaints
Since the device was going to be a ‘use sometimes’ gadget and since reading the data via USB is easier than removing/handling the tiny micro-SD card, I wanted an easily removed mounting scheme that would somehow fit on or near my already cluttered handlebars. I opted to box it in a weatherproof case, hang the case from the handlebars, provide an external power switch, and direct-wire a single connector to carry the power, serial data, and analog data.
The five direct connections are brought out to a mid-stream JST connector so the Analogger can be detached from the clear plastic case. Instead of drilling the Analogger case to bring out the new leads, it’s simply notched so the PCB can be removed for easy bench work. As noted in the Analogger Manual, I removed the two pull-up resistors R8,R9 which are installed primarily to support direct connection of thermisters. Without the resistors, high impedance voltage sources can be monitored.
There are available pads for all leads except power (+). However, the female power connector uses through-hole mounting and it is easy to reflow the solder on the end pin and slip a lead into the large mounting hole.
Normally the signal and power grounds are distinct (a resistor connects them) but in this application, they both reference CA-Gnd so a single Gnd lead was shared. This isn't the best practice in general, but since there are only 5 distinct voltage levels of interest, a bit of noise was not an issue (and the mini-XLR connector on hand was only 5-pin - no extra pin for a signal Gnd
A quick trip to Sports Authority turned up a nifty box (Lifeline Weather Resistant Case model 4430
) and a black twisty tie (Nite Ize 6” Gear Tie GT6-2PK-01
) to hang the box from the bars. An 5-pin mini-XLR connector for Crystalyte hall sensors from the parts box did nicely for the connector. I mounted the Analogger on a small piece of .060mil styrene plastic from the hobby shop (Evergreen Scale Models plain white 6”x12” sheet item 9060
) using 3M automotive emblem tape (auto stores, etc - used to mount emblems and trim on car bodies forever). A round clear vinyl bumper from Home Depot stuck on the front of the Analogger wedges it snugly into the case. The cable is tie wrapped to an extra rectangle of plastic on the bottom that acts as a removable strain relief so the case can be freed and slid down the cable by removing just the switch retaining nut.
I had a bit of an electrical loading issue with the controls when the Analogger was switched off and the inputs changed to a low impedance, upsetting the resistor dividers for bike controls. Since I had a 3PDT switch on hand, I opted to just open-circuit the two inputs when the powering down the Analogger.
The assembled unit works great. I get about 0.01v – 0.02v of noise from the monitored resistor dividers for the thumb switch controls which is in the neighborhood of 1% - fine for this application. Separate signal grounds for thermister use would likely bring the noise down near the expected 1/2bit out of 10 bits ADC resolution over 3.3v or a bit less than 0.002v.