A few days ago a friend send me an old mobile phone for using in a project about weather information in a remote location.

On the internet I found which pins on telephone are TX, RX, GND. I simply connected them to USB -> RS232 cable, when I found out that I must destroyed it last time by shortcut between ground and 5V.

I remembered about a project in which author used V-USB firmware only implementation of USB fot AVR devices to create home made USB to RS232 converter. In a few minutes I had a working converter (Thanks toOsamu Tamura at Recursion Co., Ltd.)
I connected everything and result was ... garbage. On HyperTerminal I received only garbage. I remember about using MAX232 chip for converting TTL levels to computer levels and vice versa. Tried with this chip and the same thing, of course a little bit different garbage, but still garbage and nothing useful.
So I give up for today ... tomorrow is a new day and maybe I'll have more luck. I could try connecting AVR with code for serial communicating to see if there is a problem on converter/computer or somewhere else.

Today I decided to postpone my project (RC car controlled by laptop) for a while.

I lost interest in this. It something that I often do and then get back to the project in a month or two.

Now I will have more time to figure out what to do with RFM12 transceivers that I have lying around somewhere in my room. After quick research I found out that it is a real pain in the ass. Anyway, I hope I'll learn how to use it because they weren't cheap enough to throw it away.

I haven't decided yet what wireless connection I am going to use to connect car to laptop.

I have a lot of options but every option have some advantages and disadvantages.


a) using old HP laptop - good options, i can connect webcam, additional hardware without a problem. Cons: battery has bad autonomy (about 20 minutes), weight, WLAN connection (as far as I know PCMCIA connector doesn't work, so I need to buy USB WLAN module
New battery is at least 100€ and USB WLAN module is 40€.

b) using RFM10 wireless transceiver - i have 2 transceivers at home but they are in SMD and they can be connected to microcontroller only by SPI interface which is really hard to write a firmware code for

c) using XBee - great range, a lot of resources for it but a little higher price (20€ a piece and I need two of them)

I'll probably use XBee modules but they are just too expensive. My goal is to build a car controlled by laptop for under 100€. Cost of these modules is a real set back for this project.

For a couple of days I was building a robot ... not really a robot, just a simple car, that I could controll by my laptop.

Today I got the wheels spinning, but only in one direction. I intended to use H-bridge but I didn't have both types of transistors (PNP and NPN) so I try to make a H-bridge with just 4 NPN transistor.

I learned, that you need to use electronic components as intended. You cannot use NPN transistors where you need PNP. Lesson learned for next time. ;-)

I'm back to start of the project ... Tomorrow I'll buy a cheap RC car and of course some NPN transistors or maybe MOSFETs.

I heard about DC motor driver (i think it's L293 or so) ... dunno what to buy.