My friend Wirot (codename "Jo") has been assigned to me by Dr Nipon as my personal engineer for my projects. He's an expert in electronics. When he saw my first drawing of a circuit schematics for my "blower condom" project, he proposed many changes.
I had not taken into account the fact that the blowers are motors and produce alternative current (feedback) when they slow down. As thus, we need to do two things. First, add a rectifier diode (1N4001-1N4007) to each blower. Second, isolate the circuit from the blowers using either a buffer (4DM74LS244) or a set of optocouplers (4N25-4N27). Since the 4DM74LS244 needs at least 4.75V to run, we chose to use the optocouplers instead because we try to be able to run the blowers even if we're a bit below that.
The other part of the circuit consists of the Zener regulator (see this post). Joe recommended that we build a new one using a 2N3055 transistor instead of the H1061, because it is able to drive up to 15A (!), the H1061 being limited to 1A.
Joe built and tested the first part of the circuit with me in Chiang Mai. After going back to the electronic store to buy the rest of the parts, I came back to ComPeung and soldered the rest. Everything went fine when I connected the blowers.
I then tried to connect an ATmega168 to control the blowers, but something strange happened: whenever the ATmega168 triggered the first blower to start, it would reset. I remembered that we had the same problem this summer when we were developing the project Trace (S). I chatted a bit with Sam who pointed me right back to the solution: add a small capacitor (0.1uF) between Gnd and Vcc to help reduce the noise on the circuit when the blower starts. I did it and it works fine.
I'm now working on implementing sleep mode. I'd like the module to go to sleep during the night, but also when the voltage is lower than a certain threshold (2.0-2.2V).
And lastly, my friend Joe told me he's available for being your own personal engineer for a good price. Here is his message for you:
MR.WIROT PONGLANGKA +66846154415 ALL OF ELECTRONIC CIRCUIT DESIGN