eList
The concept is the device sits on the charger and receives entries to the list using a wireless solution.
Entries can be added or subtracted using a web server application, that formats and transmits the list contents to the eLIST.
see the previous posts Beyond the Phone - eLIST progress 3 eLIST progress 2 , eLIST progress , eLIST - KOBO Touch , 5W Load Schematic
eLIST Detection
One of the parts of my challenge is to detect that the eLIST device is present.
This changes the webserver to signal to anyone trying to add items to the list, that they are too late, or that for some reason it won't accept them.
In order to achieve this I needed to modify the transmitter slightly.
RPi GPIO
The Raspberry Pi has a GPIO (General Purpose Input Output), but it has no protection and connects directly to the processor chip.
Hence a false move and you may have damaged your RPi permanently.
I've always been trained that no IC should receive a voltage higher than its supply voltage (unless specially designed), and so the thought of feeding 3v3 into the GPIO from the transmitter, made me concerned.
The better method is to feed the output from the transmitter into an opto-coupler, and the opto-coupler output can pull down the GPIO pin.
This provides complete isolation between the two devices.
Adafruit
I remembered some time ago that I brought these neat prototyping boards from Hadley at Nicegear, that are designed to be used in the wearibles (hence the rounded corners).
They also have the advantage that every connection is connected to every hole, so rather than add links, you remove them.
It takes a bit of thinking to make sure you remove what you want .... next time I'll draw the paths first.
The circuit is relatively easy, two optocouplers fed via 470 Ohm resistor from the D5 and D7 leds outputs on the transmitter.
These then connect via a header plug to the RPi, GPIO pins 22 and 23.
I have yet to decide where to mount this, but as you can see its small enough to go anywhere.
Hopefully that completes the hardware modifications.
Software.
I haven't had any more time to do anything much since my last blog, and I'm tied up tomorrow night, so I may not be able to do everything I want before the challenge finishes.
It has highlighted that I need to spend some quality time on web interface programming.
I'm stuck with the KOBO characteristics and how it handles the web browser application ..... but it will work.
While its desirable to use the ePaper devices, the concept will work for a tablet or other device.
Since it sits on the charger most of the time, the battery is unlikely to go flat during the shopping trip, and 7 inch tablets are very cheap, much easier to hack, and can run an app for this.
So the plan still remains and the end goal hasn't changed .... just the means of getting there.
Thanks again to our sponsors ... Wurth, Texas Instruments and element14.
If you wish to vote the poll is here Community Choice - Beyond the Phone Challenge
Mark