Step 3: How it Works: Receiver

Once the transmitter goes high or low, so does the receiver's data line, so to send data packets all you have to know is the distance between the pulses, and where the data packet starts.  When the RX line goes high, the Arduino's interrupt is triggered, and it starts reading data. It waits 0.5 ms, checks if it's high or low, waits again, and so on; high = 1, low =0, like before. The bytes are sent in descending order, so each bit carries half the value of the previous one. If it reads a start code, it will continue reading data; otherwise, it quits. After it has stored all the new data, it quits the interrupt and spends the next 10ms updating and running the servo and motors until the next packet arrives.

You can see in the code that every time the Arduino successfully recognizes the start code, it blinks the LED that comes pre-installed on pin 13. This makes it easy to see it your radio is transmitting properly -- the white light should be flickering on pretty much continuously.

         The Arduino scales the motor values to be higher the further the potentiometer is from 128, with a maximum amplitude at 0 and 255 (raw values). The direction (reverse / forward) is determined by the two digital inputs that go into the H-bridges ( the motor driver circuits -- I used the design from Mark Tilden's site). Pull one side high, it goes reverse, and the other side makes it go forward. That might sound mysterious, but look at the schematic with all the transistors laid out nicely and it'll make sense. The H-bridges I built can be seen in the picture.

Anyway, the motors draw a relatively large amount of current, so you can't power them directly from the 7805 -- they draw from the 7.4V battery through transistors. The servo and radio, however, do run off the voltage regulator. You can see all of the receiver parts connected together above. It is a bit of a mess, in the name of reducing weight.

You blimp looks awesome, only the code is without any doubt the most incomprehensible code I have ever seen! I can't make heads or tails from it. Could you explain the how te code works? I really like the 433 MHz set I got, but I haven't found a clear code that I can adapt to my homemade rover. <br> <br>Thom
Darn, I have been trying to figure out your code for quite some time, IT-IS-SO-SIMPLE, I have tried to use virtualwire but then I can't use the servo library (they hate each other). Thanks for sharing it!
when I first read the title I accidently read &quot;Hydrogen bomb.&quot;
Nice work on this project! I had the same 433 Rx Tx units and could never get them to communicate properly! Definitely one of the best troubleshooting sections I've read!
this soo reminds me of the hindenburg. tho to be fair, hydrogen had nothing to do with the explosion. zinc paint(?!) was the problem. <br>very cool project. <br>tho 433mhz might not be legal in USA, but even a toy car with arduino could work
You are my hero. I have tried filling a smaller blimp with hydrogen in the same way, but using only very small amounts of lye (five attempts with no success). I would love to build a setup like this some day, especially one using a hydrogen fuel cell for power. One question: does the water buffer remove any steam or water vapor from the hydrogen entering the envelope? I always worried about getting water in it. Thanks for a very informative 'ible.
You're right to be worried about water vapor. It will only be a problem if you let the reaction get too hot, which will make it start steaming or even boil if it gets out of hand. If you make sure it doesn't get more than a little warm ( I dunno, 75 deg F), the water vapor will be negligible. If you're really worried about it, you could try running the gas through a percolator to cool it down before it enters the envelope (meaning some of the vapor would condense out). The buffer I have is mainly to prevent any water in liquid form that bubbles up from getting close to the envelope. Don't give up on lye!
Awesome. Love the chemistry lab details and the troubleshooting section.

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