CC2500 Project (Part 8) - Downsizing

I received my PCB's yesterday (From Laen at dorkbotpdx.org, of course!). I spent last night attempting to solder all the surface mount components (and for the most part, failing miserably). I need to get some solder paste and a small oven for the next batch...

Those components are tiny!

After soldering all of the passive components and msp430's, I began the first set of tests. First I checked to see if all of the connections were good with my multimeter. Once I fixed any problems I found there, I tried powering the board and connecting with the programmer/debugger. Surprisingly, it worked almost immediately! (I had to connect power to the correct pins first...)

This is why I like my glass desk.

The next test consisted of flashing the two LED's. Unfortunately, only one of them worked... I put together two devices, but LED1 didn't work on either one! I decided to call it a night then. After getting back from work today, I continued my debugging session. Turns out that one resistor wasn't soldered correctly (my multimeter test worked because I was pressing it down with the probe) and the second was a badly soldered LED.

Entire device MSP430 + CC2500 Radio

I continued the same test by toggling all of the IO pins (Port 1 and 2). I looked at each one with the oscilloscope to make sure it was toggling correctly. As soon as I started, things went downhill. Some pins toggled, but most didn't. I went back and re-soldered all of the msp430 pins and tested them again. It was better, but half of the pins still didn't toggle. I decided to probe the microcontroller pins directly, but they weren't doing anything either. It had to be a software problem. It turns out that I was only toggling pins 0-3, and not 4-7. Once I realized my stupid mistake, I corrected it and everything started working.

New device in front of prototype it's replacing.

The final step consisted of soldering the CC2500 radios. Unfortunately I didn't think my design through very well, since the radio modules have the crystal oscillator at the bottom, so it kind of sticks out at an angle. I changed the wireless RGB LED controller code to run on the msp430g2412 (which is what these use) and re-programmed them. Amazingly, the radios worked on my first try.

Look at all that free space!

I decided my old RGB LED controllers were taking up too much space on the breadboards, so I replaced them with the newly created modules. They take up very little space and work just as well. I'm thinking of making the switching DC/DC power supply just as small and hopefully integrating it with the current device.

Another device next to the components it replaced.

Now that I have a semi-decent platform, I can start working on writing some awesome radio libraries. (Once I put together more radios of course...) I want to have a full home-automation system going in a few months. I'll keep posting updates here.

CC2500 Project (Part 7) - More Lights and Power Supplies!

Here's another quick update (with lots of pictures and a video!) I ordered another RGB LED strip from adafruit in order to test how my system works with multiple devices. I don't have my PCB's yet (I shipped them to NY by mistake...), so I had to build everything on breadboards.

My messy work space.

The main problem with my previous design is that it required two separate power supplies. The LED strip runs off 12v, while the microcontroller and radio run at 3.33v. I had a couple of MC34063A DC/DC converters laying around, so I figured I'd make a 12-3.3v converter. I also had an LD33V linear regulator, so I decided to try them both.

Device with linear regulator (left) and DC/DC switching regulator (right).

Unfortunately, I didn't have the exact parts required to make the switching regulator, so I had to use the closest available. This produced an extremely noisy (± 400mV) output, which resulted in a non-working microcontroller. I was able to temporarily solve the problem with some decoupling capacitors, but I still need to get the right parts to make it more stable. What happened was that the microcontroller would start and then just hang or reset at random. At first I thought it was a code issue, but then I looked at the power supply... I'm glad I bought an oscilloscope, otherwise this problem would have been pretty hard to solve.

That's a huge 0.33 Ohm resistor (It's all I had...)

Since the DC/DC converter was not behaving too well, I decided to use the linear regulator with the other circuit. Dropping 12v to 3.3v with a linear regulator produces a lot of heat. I had to get a heat sink, otherwise I would burn my hand if I touched it. It's a huge waste of power, but it works for now...

Dropping from 12v to 3.3v generates a LOT of heat. (Thankfully, I had a heat sink)

In order to drive the second LED strip, I had to put together another RGB LED driver board. It's just three MOSFETs, along with some resistors and BJT's to drive them. I connect the 12v power supply directly to these, and then connect it to the microcontroller board's power supply. The next thing to do will be to have them all on the same PCB...

RGB LED Driver (There are some surface mount resistors and transistors on the other side)

So what did I end up doing with these? Well, I put one on top of a shelf, and the second under... Ok, I don't know what it's called. It might be a kitchen counter-top, but I'm not sure. Here are some photos that will hopefully make more sense.

Shelf plus LED strip.

I'm not sure what that is called(counter-top?), but that's where I hung the second strip.

I tried getting a video of the whole setup, but my camera doesn't seem to like low light situations. It looks much better in person!

CC2500 Project (Part 6) - Reorganizing

This post is mostly about software, so I'll keep it short.

I re-arranged most of the code so it hopefully makes more sense. My goal is to make the main code hardware agnostic. That way if you want to use a different device, you just change which drivers you're using, but your main code stays the same. Eventually I'd like to be able to support multiple devices from multiple manufacturers.

For a much better description, check out the page (and code) on github here: https://github.com/alvarop/msp430-cc2500
(The README file should have some information)

To keep things interesting, here's a quick video on what I was able to do with the current setup. The RGB LED controller(msp430g2452 + cc2500) is wirelessly connected to the PC(msp430g2533 + cc2500 + usb-to-serial converter).

CC2500 Project (Part 5) -- SPI Problem Solved!

So I wrote last week about getting UART working on the MSP430G2533 but having major problems with the SPI interface... I was so frustrated that I caved in and purchased a Salae Logic analyzer. It finally arrived today, and I had a chance to test it.

Salae Logic in action!

As soon as I opened the box, I connected it to sniff the SPI lines between my msp430 and cc2500 radio. It took me maybe 10-15 minutes to set up everything, including the Salae software to decode SPI on the fly. I ran my radio-setup code and observed the logic output. It seemed like something was happening, but it wasn't quite working.

First capture with msp430g2533

To get a better idea as to what it should look like, I connected my msp430g2452, which had a working SPI link with the radio. The first thing I noticed was an error saying that the clock polarity was inverted. Aha! So the SPI clock on the 2533 was low when idle, while the specification says it's supposed to be high.

So I went into the datasheet and figured out how to fix the clock problem.

'Correct' capture with the msp430g2452

I tried it again and, not surprisingly, it failed. Looking more carefully at the MISO/MOSI lines, I realized that they were backwards! Turns out that the SPI IO pins do not match between the msp4302533 and the 2452. I swapped two wires and everything started working!

While I was really happy I fixed the problem, this means that my previously mentioned PCB will only work with one of the two devices. My plan is to use the more expensive 2533 as a PC-to-radio bridge, since it has both a hardware UART to talk to the pc and hardware SPI to talk to the radio. The cheaper 2452 only has one SPI to use the radio.

Launchpad with cc2500 Radio and Salae logic

In the end, I'm still happy. The Salae logic was extremely helpful and easy to use. It took me less than an hour to solve a problem I hadn't figure out in two days! Now I will be able to focus much more time in coming up with good radio libraries, instead of debugging silly problems.

CC2500 Project (Part 4)

I haven't been working on this project lately, but I finally got back to programming yesterday. I got the MSP430G2533 which has both hardware UART and SPI. This one will act as a bridge between the PC and the CC2500 radio. It could also be used to drive a serial LCD.

I managed to get the UART working, but for some reason I'm having trouble with the SPI communication with the radio. I've been wanting to get a Saleae Logic analyzer for a while. Now I have a reason!

On the hardware side, I put together a breakout board for the MSP430 and CC2500. It only has a few passives and two LED's along with the MSP430 and a header for the CC2500 module I've been working with. I put them on opposite sides to save space, but that caused some problems.

I want to have the radio and antenna exposed, which means the MSP430 needs to go on the other side. Unfortunately, this means that the pins are all backwards(Top-right is pin 1.) I'll just have to keep that in mind while breadboarding.

Hopefully I'll get the Saleae Logic soon so I can iron out these SPI problems. Once that's done and I have these boards, you should start to see some much nicer projects (and better code!)

CC2500 Project (Part 3)

Here's an even smaller update!

Since the MSP430G2452 doesn't have a hardware UART, it's not very useful in communicating with the computer. I could use the bit-banging method to get 2400baud, but I didn't feel like figuring it out.

For my thesis, I implemented a serial-to-radio repeater using the EZ430-RF2500 and a USB-to-serial converter. I was able to modify the code to get it working. It ends up being a 19200baud link. For some reason, I can't get the processor to run at 16MHz without it giving me problems. Since I don't wan't to figure those out now, I'm running it at 1MHz, which prevents me from doing the usual 115200baud. (Not that I really need that speed.)

I then wrote a quick processing sketch to capture audio and send RGB values out the serial port to the microcontroller.

In short, I can now sync the lights to the music wirelessly!

Here's a quick video demo (As you can probably tell, I'm really happy it worked!):

CC2500 Project (Part 2)

Here is a quick update on the project's progress.

Today I was able to get the radio libraries working better and actually set up constant radio communications across a room. I also wrote an RGB led controller using PWM and combined them together.

Here's a brief video of the result:

So far it's just one microcontroller generating RGB values and sending them to another one. Now I need to work on getting the PC to talk to the first microcontroller so I can control the lights with my computer.

Here's a demo of what I want it to do later. I have it working in the video, but it's fully wired and uses an ARM Mbed for control.

CC2500 Project (Part 1)

So I've started working on another project... This one includes microcontrollers and radios. The "goal" of the project is to have a very cheap 2.4GHz radio module and libraries to use it. I used the CC2500 radio module for my thesis project, but it was part of the EZ430-RF2500 development kit. The kit itself is nice, but at $20/device, it's not the cheapest.

My first though was to build my own board. I decided against it for several reasons. The first being that the CC2500 only comes in QFN packaging, which would make it a pain to hand solder. The second is that I have no experience designing RF circuits, which would probably result in the thing not working. The last reason is that I found a better alternative.

Turns out that the CC2500 is also used in some PS2 Guitar Hero controllers. They have the CC2500 chip on board and all the passive components (plus antenna!) I figured that would be much easier to work with. It has an SPI interface, so it can talk to most microcontrollers. The best part is that the whole thing costs less than a single CC2500 chip! I was able to get the whole thing for $1.80. (If you buy more than 1000, it only costs $1.35!) The only caveat is that the module has to be purchased from the manufacturer in China, which, at small quantities, makes the shipping a bit expensive.

CC2500 module with breakout board.

Since the header for the board has 0.05'' separation, I had to make a breakout board for testing. I decided to test the radios with an MSP430G2452 microcontroller. I chose that one because is has hardware SPI and is available in 20-DIP package. The hardware SPI is really useful when interfacing to the radio at higher speeds (instead of bit-banging) and the DIP package makes it easy to work with (and fits into the launchpad).

MSP430G2452 in Launchpad with radio.

I started writing my own radio libraries. TI provides a network stack called SimpliciTI, but it's bloated and I don't like it. For my thesis project, I wrote my own lightweight radio library, but it's all set up to work under linux and msp430-gcc. Since I want everyone to be able to use it, I'm porting it to work under TI's Code Composer Studio and putting it on github. So far I only have TI's demo code from slau144h working, but it confirms that all my wiring is ok and the radios work. Since I only have one launchpad, I replicated it on a breadboard. The code just sends a message when a button is pushed and toggles an LED when a message is received.

Breadboard with second radio and MSP430.

The next step will be to get my radio libraries working and well documented...