I haven't been writing recently, but I have been working on the projects I mentioned in previous posts; the reason why I haven't actually written about the current projects is because I think it'd be more efficient to write about them once they're complete.
NTPi (aka TestPi) is nearly complete, but I just need a clear day to double check the offset
The Banana Pi & Raspberry Pi 2 box (dubbed as "2(DrivePi)" is mostly complete. If I haven't mentioned this, I kinda did now....
That's all I can remember for the moment, so if I did forget any aforementioned projects, it's not complete and still a work in progress.
One of the projects I have planned is a hold-open latch for the door of my entertainment room, which will be attached to a motorized pulley, so that I can press a button to lift the latch and let the spring hinge close the door.
My main problem with the motor is that the RPM is too high, and with the proposed latch being plastic (about 4mm thick), I'd have to hold the button for less than a second before the string is at it's shortest length (and could possibly break).
A couple days ago, I had though of using a PWM circuit to control the speed of the motor (the alternative is to reduce the voltage, which doesn't exactly help much), and I searched for one, finding a fairly simple one.
I first looked at an old IC that I used for a correspondence electronics course (I was trying to make a remote-controled "flashlight"), and found that it was the 555 timer IC that I needed for the PWM, which was nice. I then thought about the 100nF (.1uF) capacitors that I would need and remembered that I can reduce the capacitance of capacitors in a series - unfortunately though, it's impossible to make 100nF from values 1uF and over.
At work, I had found some stray 100nF SMT capacitors in 0603 and 0805 case codes and took them home with me to see if either would be large enough to use, and luckily, the 0805s were. I also grabbed an unused 10k variable resistor even though the schematic on the page uses 100k (I figured it wasn't going to be a big deal).
The schematic also called for 1N4148, which I was very lucky to find in the pile of salvaged diodes I have (I thought I had substituted for T4148, but it's the same thing).
After getting it built, I first tested the circuit with an LED to make sure the 555 IC wasn't dead, and luckily it wasn't, then changed the LED out for a 5.9V motor (I was using USB power, so I was under-volting it a bit) to check the actual PWM cycle. Needless to say, it worked and I could tell the PWM was working because of the screeching noise at the lower setting (anti-clockwise). While I could take it to work and test it on the oscilloscope, it's not really necessary, since I already confirmed that it works.
The board I used was the same RadioShack board from the previous 555 IC, and although it works, it's a cheap board (the pads come off with just the right circumstances. I also used some salvaged 0 ohm SMT resistors and some 24 AWG wire (from a Cat5e cable) to make the necessary jumps.
I'd like to make a good board for it, but from my experience with the PCB Artist program from Advanced Circuits, it still seems a bit daunting. I probably will eventually, since it'd be nice to have the capacitors on their own solder pads instead of between the solderpads on the underside of the board (not to mention I can just have traces running around the board instead of jumpers). Once I do though, I think OSH Park would be my best bet price-wise.
The PWM circuit page says that I can adjust the frequency by changing C1, but it'd be easier to just stick with the 100nF... Though I might play around with it later.
While the circuit itself is complete (in a usable state), the project that it's part of is not.
That's all for now, hopefully the weather will clear up enough soon so I can get the NTPi project up here.
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