Skip to main content


This section allows you to view all Topics made by this member. Note that you can only see Topics made in areas you currently have access to.

Topics - blarson

General discussion / Problems with Dangerous Prototypes KICAD parts
When I was doing my first project in Kicad, I've found problems with the layouts in the dangerous prototypes library.

Various TO-220 have the pins numbered 132 rather than 123.  This means when you use them with transistors from other libraries the signals will be routed to the wrong pins.  I wound up using an outline with a heatsink to avoid this problem, but this wastes board space since I won't be using a heatsink.  They may also have the problem mentioned below.

The dp_devices-TO-92 has solder mask over the solder-side pads.  LED-5MM also has this problem.
Project logs / BatLev -- LiFePo4 Cell Balancer
Lithium Feric Phosphate cells are a lower engergy density variety of lithium-ion cells that don't have the fire hazard and short life problems of the more common li-ion cells.  They are popular for electric vehicles and are gradually making their way into marine and RV applications.  When used in series (for higher than 3.2 volts), they need protection circiutry to avoid over-charging a cell.

This project is a cell balancer, that acts about like a zener diode.  Over the set voltage, (variable over a small range) it acts as a load on the cell, turns on a red LED, and has a opto-isolated indicator for turning off the charger.  The TL431A is followed by a two-transistor amplifier for the 3.3 ohm 5 watt load.

This is the first project I did using kicad, and I had some problems including the to220 outlines from one of the part libraries I used had the pins numbered strangly, fortunatly I noticed this and switched to a different outline before I ordered the boards.[attachment=0]
Hardware biz / When do I get regulated
I have some projects at various stages in development that I am considering selling.  At what point do I need to worry about things like FCC testing, avoiding lead solder, etc.?  (I currently use 63/37 solder, and my 2 lbs should last years unless things get unexpectedly popular.)  If it matters, my legal address is in Oregon.

The more complicated and expensive product I am contimplating will likely involve customizations and installation, so will be in very limited quantity.  I'll probably open-source both the software and my custom hardware.
General discussion / off-board i2c connections
For a project I am contimplating, it looks like having some peripherals connected by i2c on other boards would be useful.  My questions are:

Is there any standard connector for i2c?  If not, I think a 5-pin one would be best with ground, data, clock, +3.3v, +5v.  I'd use one connector on the control board for each channel, two on the peripheral boards to daisy-chain, and plug the terminator (to 3.3v) on the last board. 

What size/type of wire?  What lenght limitations?  I realize that it depends on the speed of the i2c bus, and the capacitence and interference may dominate the lenght limit.
General discussion / selecting a microcontroller
How do you go about selecting a microcontroller for a project that starts off as a hobby one-off, but if it works out may go into small scale production (dozens or hundreds).  Cost of the actual chip doesn't matter much as long as it is less than $10 or $20, the project will be dominated by development expenses.  I'm leaning twords arm for several reasons, but the packages are somewhat scary for someone with my (lack of) solder skills.  Selecting which arm is also a problem.
General discussion / Source for BA15s plug?
Does anyone know of a source for BA15s plugs (not sockets) that is not rediculously expensive or have huge minimum orders?  As light bulbs that use them can be gotten for $0.50 each retail, I think $0.25 each would be reasonable, and I want  maybe a dozen (or 100) for prototypes, and then ordering them in hundreds or thousands for production.
General discussion / Using IR remote as keypad interface
For hobby projects that need more than a couple of  buttons, keypads tend to use many IO pins and are getting harder to find on the surplus market.  IR receivers are cheap and use a single input pin.  IR remotes are readily available.  Many of us have working remotes from dead devices, the local charity store has a basket of them, and it should be possible to get overruns for low production quantity projects.  LIRC or the USB IR toy can be used to learn the codes of a random remote.  What is missing is the libraries to take this info and use it.

An example of such a project would be an improved kitchen timer, with stir times as well as total cook time.