So in the sort of tutorial I wrote about ORC-KIT I mentioned that it was possible to use other boards instead of Adafruit’s friendly motor shield, and in fact, there was space in the board for a couple of very cheap and widely available L9110S Dual H-Bridges, which should give you more control over the build, and “free” some precious Arduino pins that you can use for extra sensors and actuators. You can actually change the Arduino for something else, but that’s beyond the scope of this post.
H-Bridges are simple circuits that allow you to control the flow of current through a “load” with 2 control signals (A and B). When the load is a motor, you can make it spin forward, reverse or stop completely by changing the digital values on A and B. H-Bridges normally have an ENABLE line as well, which you can toggle yourself or leave permanently “ON”. Controlling the speed of the motors is easier if you can turn each bridge on and off quickly using PWM pulses applied to the enable lines, but that’s not always possible. The L9110S boards don’t have an enable pin, for instance, so we will need to manipulate only the 2 basic control signals to drive our motors if we use this controller.
Each of these Dual H-Bridge modules can drive 2 motors and has a 6 pin header for the 4 control signals plus power.
You may remember the small soldering fume extractor I designed a while ago. It has worked really well since I built it, and it’s made my soldering work a much more pleasant experience.
However, during the time I’ve been using it, I’ve discovered a small aspect that could definitely be improved. Because of the way it works, when the fan start working it “sucks” the carbon filter a bit towards the blades. As the distance between the filter and the fan blades is no more than 2mm and the filter itself is not rigid, the carbon surface “bends” and touches the spinning fan, which causes the blades to pull and cut fibers from the filter. You can actually hear this happening when you turn the unit on with a reasonably new filter.
This stops after some uses, as the filter becomes thinner and less dense from all the fibers it has lost. This doesn’t prevent the extractor from working, but it certainly reduces both the efficiency and the lifespan of the filter.
To solve this I designed a small plastic “grill” that would hold the carbon filter in place, separating it from the fan.
Carbon filter holder for my soldering fume extractor.
Earlier this year I embarked on the journey of designing a simple but expandable robot that any electronics enthusiast could build. I knew several nice kits from brands like Lego, Makeblock, OWI Robotics, etc, but I considered them to be normally either too expensive or too simple and limited. There are also many generic unbranded kits on eBay which suspiciously have all pretty much the same design but vary mostly in their debatable choices for hardware and layout.
I wanted to do something flexible but not too expensive nor flashy, much like the unbranded kits, but with better design practices in mind, and engineered to be heavily customizable.
Fully assembled Vanilla ORC-KIT with some extras.
Not long ago I purchased a few 320×240 touchscreen displays from ebay that looked pretty decent and were also fairly cheap. They conform to the Arduino shield form-factor, so they snap directly onto any standard Arduino board, making them really easy to test and use. They also have an integrated microSD slot (connected to the same bus used by the display controller) which is a nice touch and widens the number of possible applications for these modules.
As seen on literally every eBay listing that sells them.
Of course the displays didn’t come with any code, and the most reasonable thing you’ll find online to make them work is Adafruit’s TFT-LCD Library, which includes support for a number of different controllers, and is fully compatible with their very own and versatile GFX framework.
I used to have a small desk clock that I purchased for a trip. It was cheap but it had some really nice features that I quite liked. It had large digits that I could see from my bed each morning, and it was also able to measure and display the current room temperature, which I always thought was incredibly cool for a clock.
The problem is, that it required a lot of batteries to work; 4XAAA for the fancy LCD backlight and soothing RGB glowing action, and 2xLR66 (button cells) for keeping the thing ticking and actually displaying time and temperature on its LCD screen. It worked reasonably well, but it was running through the batteries way too fast, in my opinion.
I didn’t really care about the AAA batteries dying in a month, because I could always use rechargeable batteries there, but the small LR66 batteries were killing me. Replacing them each 5-6 months or less wasn’t really a pleasure, especially since it meant setting time, date and alarms all over again, every time.
So I adventured in the journey of building my own clock. My main objective was to keep the number of batteries low, while also having the nice features of my previous clock, like the big numbers and the temperature readings.
SPOILERS: This is what I ended up making. No, it’s not a bomb.
So in a previous post I’ve discussed how to communicate with a custom HID device using libhid and a Raspberry Pi running linux.
This post is a sort of sequel. I’ll talk about some of the issues and nuances I found when working on a more complex (but related) project; In this case a Composite USB Device that I had to implement on a PIC 18F4550 microcontroller.
I wanted to add a temperature sensor to a project I’m working on, and while I already had selected the perfect IC for the job, I decided to test a couple of other options I had, to see how they fare in comparison. I was originally going to compare only 3 sensors; the popular LM35, the not-so-popular LM335 and the kinda obscure TMP75, but as I started writing this post I remembered I got a Dallas DS18B20 as part of kit of sensors, so I added it to the mix to balance the digital-to-analog ratio of this comparison.
The original 3 sensors I was going to test.
If you have any experience with a soldering iron, or soldering electronic components in general, I’m sure it will come as no surprise for you that the “fumes” produced by the process are not exactly good for your health. They can be quite harmful in fact (** depends a bit on the chemical composition of the solder you use). Even if they weren’t, they are -at the very least– annoying as hell. They always find their way to your eyes and throat in the most unpleasant ways.
I discovered some time ago that a device specifically designed to cope with this issue existed, and it’s been in the market for a quite a long time. This unbelievable product of heaven-sent technology and engineering is unsurprisingly called Soldering Fume Extractor (I bet you didn’t see that coming) which is nothing but a pompous name for a small desktop fan with an active carbon filter.
It’s been with me for more than 10 years.
Back in the ’80s, Casio produced a line of calculators that was sold and advertised as “pocket personal computers”. This branding started with the PB-100 I believe, but the device concept started with a previous model, the FX-702P, produced in 1981.
While by today standards that claim seems a bit of an stretch, it held quite a bit of ground back then. These calculators featured a BASIC interpreter built-in, and internal memory to store user programs. They also featured a proprietary port/interface that allowed some Casio peripherals to be connected to the device, like a printer or a cassette drive. Personal computers back then were not much more than that.
The FX-850P model released in 1987 -and other calculators that followed- were a significantly step forward since their peripheral options (via the Casio FA-6 Casio interface) included standard Centronics parallel port and RS-232 serial connectivity, both ports widely used in computer hardware.
The FX-880P, released in 1990, was (I think) the last device in this line of Casio personal computers / calculators, and was basically a FX-850P with 32KB of RAM (instead of just 8KB).
When I was a kid I used to see this calculator in store catalogs and magazines and always wanted to have one. Many years later, when I was old enough to purchase my own stuff, I was finally able to get one (second hand) in pretty good condition, and I still use to this day.
As part of a bigger project (that I’ll reveal later) I set on the journey of designing a simple “keyboard”. It needed to have enough keys to be usable as a general purpose input device (so it requires alphanumeric chars, common symbols, ENTER, ESC, etc) and preferably built around components I already had (like the bunch of 6x6mm push buttons that I don’t seem to be using fast enough).
Taking old devices and early computers as reference, I went with a 40 keys design (a 5×8 button matrix), arranged in a 10×4 distribution (internally 4 straight rows of 8 buttons, with the “fifth row” split into the 2 extra columns).
I spent some time doing a keyboard layout with Inkscape, trying to fit all the keys I wanted in a way that made sense:
Matrix Keyboard Layout