I finally think I have a version of the motor driver that I like. I tweaked the traces around the 470uF cap to make the ground path better. I also changed the nSleep jumper header from a 2-pin to a 3-pin. The user can hard wire the nSleep high or low.
I finished up the PCB for the Motor Controller Booster pack. The PCB is all open source and you can download the files here.
Files (Eagle V6)
This is a Low Voltage, 2A motor controller BoosterPack for the Ti LaunchPad. So far I have not found a motor controller yet so I decided to make one. This is the first in many BoosterPacks I will be designing and selling. It uses the Ti DRV8833PWPR Dual H-bridge Motor Driver chip. The chip is capable of 2Amps per motor channel and a motor voltage from 2.7V to 10.8V. Logic voltage for the DRV8833 is 3.3V which makes it a perfect match for the MSP-430 LaunchPad.
The BoosterPack has the nSleep pin broken out from the DRV8833. Using this pin will put the DRV8833 to sleep to minimize current draw. If this pin is not needed or the LaunchPad is lacking I/O there is a jumper to pull the nSleep pin high.
This circuit is designed around the MCP73837 chip. There are a couple different versions of this chip which allows the same PCB have a charge cut off voltage of 4.2V for normal lithium batteries and 4.35V for high capacity lithium batteries.
4.20V – MCP73837-NVI/UN
4.35V – MCP73837-FCI/UN
It charges via USB at a rate of 500mA or an external power supply rated at 5-6V at 1A. I would use a power supply at a rating of at least 1.2A for this charger.
Added a micro usb plug to compliment the mini usb plug and DC power jack. Made all the passive parts 0805 size to make the board easier to assemble. Tweaked the mounting holes a bit as well.
Files (Eagle V6)
Put together the project page for the Single Cell Lithium Battery Charger Circuit.
This project is open source and all the files and part lists needed to make the board are located on that page.
Already updated the PCB to Ver1.1. Forgot a ground trace.
This circuit is designed around the MCP73837 chip. There are a couple different versions of this chip which allows the same PCB have a charge cut off voltage of 4.2V for normal lithium batteries and 4.35V for high capacity lithium batteries.
Here are the eagle files.
PCB V1.0
Schematic V1.0
First 8 PDS V1.1 are built!
I only have 2 out of the 10 left from the initial run of V1.1. The first batch for those that have already ordered will be shipping this Friday. PDS V1.2 already has some design changes that will increase the boards functionality and usefulness even more without adding to the cost of the final product.
If you want to grab a the PDS V1.1 for testing send me an email. Cost is $25+$3 shipping which is the at cost price to make the PDS in low quantities.
V1.2 will hopefully be the full production version and will retail at $40ish.
Have a suggestion or want to discuss the PDS? Join our forums!
Here is some analysis of the power lines and noise on the board. These measurements are taken with no load on the I/O besides what is built in on the board. Pins 29 and 28 run the EEPROM in I2C mode on boot to load the program into the Propeller.
With the Propeller doing nothing the board takes 7mA on the 5V line. Flipping all the ports as fast as the Propeller can do it at takes 20mA at 5V. Turning on all the cogs (8) and flipping the pins takes 94mA which is almost 1/5th the power budget of the USB spec (5V 500mA). During these measurements the board was powered with a dedicated lab power supply.
Here is the worst case noise analysis of the board. This is when all cogs are on and flipping all the I/O on and off to surge the power lines. Power is from my laptop USB port.
The top line is the 5V line from the USB port. This is expected to be fairly clean. The scope showed that it was relatively flat with with very little peak to peak action. This shows my laptops 5V line is a relatively good power source for the PDS.
The bottom line is the 3.3V line that is produced from the regulator on the PDS. As you can tell it is not level and oscillates a bit. The peak to peak is at 1.44V which is a very dirty power line. To fix this I added a 1uF capacitor to the 3.3V line which generated the following power signals.
The 3.3V line now has a peak to peak of 160mV which is pretty good. I tried a 10uF capacitor to see if this could be improved but I received the same results. The PDS V1.2 will need to have a 1uF capacitor added to the board before production. This will be added via dead bug technique to the PDS V1.1 boards.
I just finished soldering the first Prop Dev Stick and tested it. After installing the FT232 drivers I was able to program the propeller straight from the Propeller Tool. Serial Terminal has also been tested.
I am going to be shipping a couple of these for testing. If you do embedded systems or mess around with micro controllers I would like for you to test it out. I am offering a fully working and soldered board for just the price of parts alone ($20). Simple stuff like usability, durability, and performance will need to be tested in real life scenarios before I move it into production.
Interested? Talk about it on the forums!