This application note summarizes the crystal basics, PCB layout considerations, and how to test a crystal in your application. A crystal selection guide shows recommended crystals tested by experts and found suitable for various oscillator modules in different Atmel AVR families. Test firmware and test reports from various crystal vendors are included.
Selecting and testing 32kHz crystal oscillators - [Link]
This is a countdown counter based on ATtiny2313, primary developed for my PCB exposure box, but it can be used for other purposes too.
The counting range is between 1 and 90 minutes and it can be adjusted with up or down buttons (high and low in the pictures).
After the desired time is set, the countdown starts by pressing the start/stop button (on/off in the pictures). By pressing the same button we can interrupt the counting at any time we want.
After the count expires we hear a beeping sound and the load is disconnected. By pressing start/stop button we reset the counter and we are ready for another lap. All actions included the time remaining are shown in the LCD display.
Pcb countdown timer - [Link]
Derek Wolfe writes:
There are a lot of hobbyists that want to design and build their own custom printed circuit boards (PCB’s). It will save you money if you’re making a lot of different board designs on a small scale. If you need to make 50 copies of something or don’t want to spend the time to make your pcb’s just order them from a professional pcb manufacturer. This procedure is for people who want to get their hands dirty and learn how to make their own circuit boards for lower cost, faster turnaround, or the simple satisfaction of it.
My method of fabricating pcb’s is based on the numerous tutorials and websites that describe the familiar ‘Toner Transfer’ process. After practicing a few years I’ve combined parts of each tutorial with some tricks I’ve learned to make this fabrication procedure. This method is useful for making single boards or panelized board designs. I prefer toner transfer vs. a photolithography based method because the copper clad boards are very inexpensive when purchased in bulk and there is no light sensitive photoresist to worry about. Photolithography is capable of better resolution and smaller feature sizes than toner transfer but it’s only a limitation for extremely small features (i.e. <0.005″ wires).
PCB Fabrication Procedure using Toner Transfer - [Link]
Make parts in Cadsoft Eagle @ Dangerous Prototypes – [via]
Eagle’s popularity is partly due to the sheer number of parts and footprint libraries available for it. Sometimes you can’t find the part you need in an existing library though, and it’s time to make your own. Making a new part in Cadsoft Eagle can be intimidating for new users, but the guide below shows how we make our own Eagle parts step by step.
Make parts in Cadsoft Eagle - [Link]
Over at Blondihacks, Quinn’s written up a really thorough post about etching your own PCBs, building on what she discussed in past documentation. There are a lot of tutorials out there about etching PCBs, but this is probably one of the most complete I’ve seen, particularly if you’re still getting to know Eagle.
PCB Layout and Etching Tips and Tricks - [Link]
In the last few years many inexpensive PCB services have popped up. It used to be that buying PCBs in hobby quantities was expensive and filled with gotchas.
Now, places like Seeed Studio can send your PCBs to the inexpensive prototyping factory in Shenzhen China, and ship them anywhere in the world at great prices. You get two-sided PCBs, with the works, starting at $1 per 5x5cm PCB. Turnaround is a few days, worldwide shipping starts at $3. It’s a happy day for electronics hobbyists.
Other services like DorkBotPDX and BatchPCB pool multiple orders so the group benefits from bulk pricing. Enough people are using these services that turnaround is quite fast. DorkBotPDX offers signature purple PCBs that have become quite popular.
HOW-TO: Get your PCBs manufactured - [Link]
If you need to know the exact length of a trace in Eagle — for differential signals, for example, or if you have a high-speed data bus like on SDRAM and you’re not using a buffer so you need to make sure all the traces are the same length, and make sure they’re no too long for the strict timing constraints, etc. — Eagle has a nice little ULP script that will display some basic information on every trace on your PCB, including the maximum theoretical current you can draw through the traces, etc. Just type “run length-freq-ri” in the command window of the PCB view and you should get the displayed info above! (Note that by default this ULP assumes 1oz/0.035mm copper, though this is the most common anyway.)
Eagle QuickTip: Measure Trace Length (and more) - [Link]
David Clift-Reaves has created MezzoMill, a PCB router which can provide custom single-sided PCBs in short order. He’s currently running a kickstarter to get the project into production. He writes: [via]
The conversation that I had hoped that MezzoMill would help to shine a light on is the need for individuals, hackerspaces, and schools to have small-scale electronics manufacturing facilities. I believe that there are 3 key technologies that are necessary to a modern electronics fab. First is the ability to print circuits. Second is the ability to place modern components on the circuit. Finally, the third is the ability to do reflowing.
Like the iBooks Author program, I feel that these disruptive technologies have the ability to empower people and transform an industry. Clearly all of the technologies already exist for creating these machines. People hack together various versions of them all the time. There needs to be work done towards mass producing them and a guiding vision for making all of them work together seamlessly.
I designed the MezzoMill to simplify the problem of printing circuits. It turns the experience of printing circuits from EAGLE to one like from your word processor to your inkjet. It makes the process safe and repeatable while reducing the user interaction with the process as much as possible. It is the only solution in its price range that provides this user experience to individuals.
MezzoMill: An Easy-to-Use Personal PCB Router - [Link]
I just finished writing up some of the details on DIY plated through holes. This is what the simple constant current source was designed for. This process was slightly adapted from Think and Tinker – a really great site for DIY PCB fab. The overall process is:
- Drill holes in the PCB
- Coat the holes with a mixture of water-proof ink and finely powdered graphite
- Cure the ink so it doesn’t rub off
- Dunk the PCB in the electroplating tank, apply current, and let chemistry do the rest of the work.
Electrochemically plated vias for homemade PCBs - [Link]
Retromaster has honed his PCB making skills to get professional quality boards at home. He’s successfully made double sided PCBs with 8 mil trace width, with 6 mil clearance. In his guide he describes how to etch the PCB with toner transfer, how to use mechanical vias, and hot to apply soldermask paint.
DIY double sided PCB with soldermask - [Link]