by Jeffrey Putney | Apr 21, 2015 | Fab Academy
This week my output device was to control an electric strike plate to open a door. The system reads in rfid tags through an RFID scanner and checks the keys against a master list of good keys that are updated my a local server in the room. In order to attach headers to both sides of the board it was necessary to make a two sided board. This worked will in the inner sections but around the edges the copper started to tear away from the board when I pulled it up to flip it over. This caused some pretty rough routing but the board still worked in the end. Here’s a video of it working: Design Files Eagle CAD files can be downloaded here. Arduino code can be downloaded...
by Jeffrey Putney | Apr 14, 2015 | Fab Academy
For this week I created another version of my ATTiny based microcontroller board and added a temperature sensor and light sensor. I also experimented with using a two sided board design to make routing the board much easier. Below is the schematic design with the added components: 365-1157-1-ND Phototransistor 235-1109-1-ND Thermistor (NTC 10kohm) Both of which are simple sensors that change resistance based on their designed input variable(light or temperature). By placing them into a voltage divider network we can easy measure their input level by using the analog read function of our processor. To make a double layer board I decided to use the bottom layer as just be a complete ground plane I didn’t need to actually cut it. I used the Autorouters “Select” tool to select the GND signal and set the layer cost of the Top layer to 99 and the cost of Vias to 50. This cause it to route the signal on the back plane for most of the route. I also enlarged the DRC minimum via size so that I could drill the vias with a 1/32 in bit. After the Ground plane was routed I set the Autorouter back to routing only on the top layer and routed the rest of the board. After milling the board I just had to solder in jumpers through the board at each via hole. I then programmed the board to light up the LED whenever the light level dropped below ambient light levels. Next I very roughly visualized the light level by mapping the light level to some serial port ASCII art for a real...
by Jeffrey Putney | Apr 7, 2015 | Fab Academy
Molding This week I wanted to design a cast a model that would work well for our pewter casting workshops we hold at Makerspace Urbana. I started with the Heartland Maker Fest logo and gave it a grayscale depth profile in illustrator by using the Inner Glow style on the heart path. Here is the 2D Illustrator File and SVG version. This was easy to import into the fab modules as a png file. And from there I could cut a master model out of machinable wax on the Roland Modela using the built in Fab Module setting for “wax rough cut” and “wax finish cut” cut with the 1/8 inch bit. The was used was from machinablewax.com Part# 18-0150307 – blue 1.5″ x 3″ x 7″ Once I had the master model I created soft negative mold using OOMOO 25 Silicone Rubber which has a nice and short 75 min demold time. Once the Oomoo cured it was time to cast the positive model with Smooth Cast 300. The Smooth Cast sets in just 10 min and gets quite hot in the process. The final product looked perfect! Design Files Here is the 2D Illustrator File and SVG...
by Jeffrey Putney | Mar 30, 2015 | Fab Academy
Table Design I started by creating flower table design in tinkercad. I then used 123D Make to turn the 3D model into a 2D cut plan for the CNC Machine. I was then able to import the cut file into Rhino where I had to edit the file and add drill points at every inner corner so that the pieces would easily slide all the way together. This isn’t a perfect solution but it does take care of the fact that our cutting bit has a certain radius and can’t cut all the way into corners. At this point the file was ready for the CNC Machine. CNC Time So it was off to the hardware store for some 3/4 inch MDF board. Because our Fab Lab doesn’t have large CNC Machine we had make friends with the architecture students who have a facility next door to us. They were nice enough to let use their machine for a weekend to get our projects done. We used there C.R. Onsrud 98C machine for our projects. The work flow was straight forward as they usually use Rhino for their projects and had a presets ready to go for generating files that cut MDF on the machine. I used a 1/2 inch cutting bit for the project. All I had to do was load up the file and hit run and I had a new flower shaped table. The hardest part was probably sanding all the edges. MDF cutts pretty rough and makes a mess when you sand it. But after it’s sanded it actually looks quite good. After sanding I just...
by Jeffrey Putney | Mar 16, 2015 | Fab Academy
Datasheets and Software Serial This week I read through the ATtiny summary datasheet. The main thing I learned is why the standard serial communication library can’t be used with the ATtiny44. Looking at the Arduino Serial library I saw that it mentions it uses a chip’s UART for communication. But our ATtiny’s apparently don’t have UARTs. As you can see if you search the ATtiny summary datasheet you won’t find a UART. Luckily the SoftwareSerial library has been written which implements the UART functionality in software and that library has been bundled into the Arduino environment. The Datasheet also mentioned the QTouch library which I would like to learn more about in the future. This weeks project This week the plan is to create a microcontroller board that provides 2 way communication with the serial port on the computer. I started testing by opening the Examples->SoftwareSerial->SoftwareSerialExample in the Arduino software. At first this refused to compile for the ATtiny44. I realized from the code comments that this example file was attempting to also use the hardware serial port: //Receives from the hardware serial, sends to software serial. //Receives from software serial, sends to hardware serial. So I went through and removed all the references to the Hardware Serial connection, which look like this: Serial.begin(4800); //Start Hardware Serial Connection Instead of this: mySerial.begin(4800); //Start Software Serial Copnnection In other words we only want to work with the `mySerial` object, and not the `Serial` class. 2-way Serial Communication Code #include <SoftwareSerial.h> SoftwareSerial mySerial(0, 1); // RX, TX const int buttonPin = 2; int led = 7; int incomingByte = 0; // for...
by Jeffrey Putney | Mar 10, 2015 | Fab Academy
Motivation For my final project I need a solar collection system that can charge a battery in bright indoor condition. So for this weeks assignment I chose to design a circuit and subsequent board based on the TI BQ2505 Ultra Low Power Energy Harvester Chip and a 5V boost converter chip to so that this version can at least charge a cell phone. Circuit Design The first step was following the reference designs from the data sheets and creating a schematic in eagle. The trickiest part here was choosing all the resistor values to set the battery charge values and hysteresis points. Board Layout This took some time and iterations with trying to mill the boards. The only packages available for the two chips where no lead packages that required traces that only the .010 inch mill bit could mill out. To increase the chance that traces would survive milling I had to create copper pour sections that widened as soon as they left the chips pad areas. Milling I lost a few .010 bits before I realized the set screw was too striped and no longer tightning far enough Reflow Soldering This actually went pretty smooth. surface tention managed to seperate the almost all the solder between the smallent surace mount pins though a few had the be reflowed after with a fine tip soldering iron in order to get them to seperate. It worked!!!! Even under desk lamp lighting the circuit was able to power up and provide a charge current for the Li-po battery. The boost converter was also able to start up and provide a...
