Week 12
networking and communications
Supplies, Tools, and Software
- RN4871 Bluetooth Chip
- Bluetility - mac app for scanning bluetooth devices
- LightBlue - iPhone app for scanning bluetooth devices
- pyserial with miniterm - to communicate with the chip via FTDI
Files
Overview
This week, I used an RN4871 chip to communicate via bluetooth, which I’m hoping to use to communicate between an iPhone and my final project.
Board Design
I started by using Neil’s hello.RN4871.ftdi board on this page, and also connected an LED and resistor to one of the pins (pin 7 of the RN4871), which I was hoping to be able to toggle on and off via bluetooth.
Board Fabrication
Milling
Per usual, I used the Roland SRM-20 and mods to mill the board. I ran into a few issues here this week. The sacrificial layer on the mill was really beat up after machine week, and it must have been a bit uneven because of that. Jen helped me change it after my first mill came out a bit messy.
Then I got a good one, but accidentally vaccuumed it up as I was cleaning the mill. Whoops.
The 1⁄64” endmill that I was using ended up not cutting cleanly, so it took me a couple more attempts to find one that was clean, but finally I got a good, clean chip.
Soldering
Soldering went smoothly, except that the RN4871 had really small connection points that were difficult to attach without running into the neighboring pin’s connections. This took me a few attempts.
Things finally worked out when I realized that I didn’t need to solder all of the pins, and only soldered. the pins that were connected to something.
Programming
Powering the board
I gave the board power with an FTDI connection, but I didn’t see it on any bluetooth scanner (Bluetility on my mac and LightBlue on my iPhone) and wasn’t able to communicate with it via the Arduino IDE serial monitor.
I used the multimeter and realized that some of my traces must have been bridged under the chip, so I used the heat gun to pull things up. I resoldered and ripped up a few times, but eventually saw it show up in the bluetooth scanners.
Communicating with terminal via FTDI
sudo miniterm.py
This shows the available ports. I checked the port for the USB by running this a couple times and plugging it in.
I reran the code above, this time adding the port name (/dev/ttyUSB1) and baudrate (115200):
sudo miniterm.py /dev/ttyUSB1 115200
The next part was confusing, since no CMD> prompt showed up initially. To get this to show up I typed (but couldn’t see):
$$$
By default, you can’t see the chip’s responses, so you can toggle echo on by sending:
+
Then:
SS,C0
and to reboot the board:
R,1
There were a ton of bluetooth devices near the archshop, so in order to make mine recognizable, I renamed it:
SN,JimBluetooth
Communicating via bluetooth
I used Bluetility on a different computer to scan for the chip via bluetooth, and found it. I was able to send messeges between them.