What got me started again was a chat with a friend at work on an idea that he had to control his windows shades automatically based on sun light intensity and room temperature. He indicated that this can be done via a development board called "Arduino". I had no idea what that was, but it was my ticket back to electronics. I had studied Electronics in high school, but this does not make me an expert.
Not to bore anyone here, I'm already about to do it in another blog documenting all my findings in Electronics, so I'll leave the bed time for that blog.
After much testing, I have progressed well enough to see many nice projects of a toy smart car that used sensors that can detect path blockers and also allow it to follow lines.
I decided to go with building one for "my kid" - no really I'll probably give it to him to play with it.
I wanted to create this car from scratch as much as possible, so I decided to buy only the chassis and the motors.
The above is taken from DX site, I hope the link to the product will hold:
Cool, so now I have a car, but nothing to run the engine. To drive the engines in both directions (forward and backwards) I need a device that has a logic input that can control the direction of the motor rotation and the speed.
For the speed a PWM output will do the job from any chip, so I guess I'm set there but for the direction I will need an "H bridge" to help achieve this. I decided to go with building one from a bunch of 2N2222 transistors that I have, I got around 100 of them.
After a few tries, I almost gave up and bought an H bridge IC and be done with it, but still, what was I missing. Taking a closer look at the data sheet of the 2N2222 I saw the problem, I forgot about the current gain ratio which is ~100, this is what was holding it from driving the motor, but driving LEDs it did the job just fine. Well, someone already solved this and his name is Sidney Darlington that created the Darlington Pair which is just a simple configuration of a pair of transistors that the first one drives the second one making the gain of this configuration become G^2, so if the 2N2222 has a gain of ~100, with a Darlington pair it's 100^2 = 10000.
Ok, the breadbord gave the approval of the configuration and the motors rotated just perfectly, I also hooked an Arduino board with a PWM pin to the motor H bridge circuit to get a sense of the speed control all seems to function as predicted.
I created the schematics using Fritzing:
As you see, I created two H bridge configurations to allow a control of the left wheels and the right wheels.
I arranged the components on the PCB board also in Fritzing and connected the components - now I'm ready for soldering. Here is the final product:
No comments:
Post a Comment