Whaaat? You can do that?! You need phototransistors or photodiodes silly! Turns out, you don’t. IT’S A CONSPIRACY!
Seriously though, LEDs can be used as photo detectors. It’s not as simple as using a proper photodiode, but it’s a pretty neat trick and can save you a few parts if you’re working on a budget.
So I had a chance to test my bullet counter this weekend!
I met up with two redditors this past Sunday and they let me borrow their guns for testing. I wish I could tell you that all went well, but I had some pretty interesting problems… Continue reading
If you saw this guy at a bar, would you say hello?
No? What if he shaved and took a shower? Continue reading
So, the good news is that my laptop is up and running again despite Apple designing their software to be too user-friendly to actually work (it’s cute when it’s PhotoBooth. Less so when it’s 10,000 of my photos).
The bad news is that my attempts at making a circuit board were complete failures. See results below:
Self-Monitoring, Analysis and Reporting Technology.
That’s a backronym if I’ve ever heard one.
Basically, my laptop’s hard drive is dead.
So, my attempt at make home-brew etchant before was a miserable failure, but I think I’ve found the solution:
Hehe…get it?
When you feel like doing some really rapid prototyping and don’t want to wait around for a board to come in the mail, you usually have to print a board of your own. I’ve done this a number of times (the original bullet counter was a home-printed board).
The whole process has a number of steps (which I will be going into in another post), but one of them involves printing an acid-resistant substance on a copper sheet and dissolving the un-coated copper in an acid. As I have mentioned earlier, I had some really crummy ferric chloride acid that didn’t do a very good job of etching my boards. I would usually end up sitting around for an hour or so waiting for it to etch only to have the etchant start to eat under my etch-resist while other free portions were still un-dissolved.
Ferric chloride is also kind of pricey, so I decided to try my hand at some home-brew etchant. I found a recipe online that calls for just two ingredients:
Muriatic Acid (HCL) and Hydrogen Peroxide (H2O2)
When I was at the rock gym last week, one of the staff members had some gloves with blinking LEDs in the finger tips and was dancing around like an idiot. A friend of mine was jealous and said in passing “you should invent something for me to swing around so I can go to a rave.”
Continue reading
So, I finally figured out what the deal was with my accelerometer needing to be asked twice what the value was.
As it turns out, I wasn’t actually giving the chip time to reply. I thought the micro would automatically handle receiving the data value, so I all I had to do was send the ACK at the end. In fact, the command that sends the ACK actually tells the micro controller to wait until the entire data byte has been transmitted, and then transmits the ACK.
So, when I was storing the value before sending the ACK, I was storing the value that I originally had in the register (the address of the accelerometer chip) and then waiting for the data and finally sending the ACK. Now, I’ve changed it so that it waits for the data and sends the ACK before storing the data value in the register.
How did I figure all of this out? With an O-scope! I simply modified my code so that it would give me a voltage spike on one of the output pins while it was reading the data from the register. What I noticed was that it was spiking before it was supposed to. Here’s an example of what I mean:
