Prop Board with Fuses on pins
John Kauffman
Posts: 653
Does anyone make a prop board with auto-reset fuses on the pins and capable of taking voltages up around 20v? It would be great for classrooms where I frequently get wiring shorts.
If not, there is an opportunity for someone. http://ruggedcircuits.com/html/ruggeduino.html
If not, there is an opportunity for someone. http://ruggedcircuits.com/html/ruggeduino.html
Comments
Wiring shorts to what? I normally protect power with a tiny 1206 PolySwitch, there are various sizes and current ratings. I find fuses a real nuisance because you have to provide for replacement. A PolySwitch just trips and resets automatically after the load is removed. As for I/O pins they don't normally have a problem if they are shorted to each other but a simple series resistor of around 220R is all I normally use and so it doesn't matter if they are shorted to power or ground, higher voltages are a different matter though.
What you need to do is to put a buffer chip between your Propeller i/o and the real world. The Hex inverter (a 74ls04) is the usual solution for outputs or inputs. If you need bi-directional devices, they can be had with 4 bits or 8 bits in parallel.
I am wondering where this 20 volts is coming from and intended to go to.
Parallax even sells a text for the Propeller that discusses this approach. Programming the Propeeler with Spin -- A beginner's guid to Parallel Processing by Sandhu.
You could also do that the Ruggeduino does, but with lower zener diodes... about 3.4 volts. Parallax has build protected BasicStamp boards in the past with 220 ohm resistors on all the i/o. That works up to a point.. but there are situations where it gets in the way.
You can buy 8x 220 ohm resistors in a parallel in a DIP package and easily deploy them with the Propellers 40 pin DIP on a breadboard. The zeners are a bit more of a hassle to wire into a breadboard as one end has to tie them to ground.
Here is some info I googled:
From http://forum.arduino.cc/index.php?topic=160065.0
Not sure if this is helpful, but the IO protection on the ruggeduino is simply a 24V 220 ohm PTC thermistor (PN PRG18BB221MB1RB)
This should be an equivalent through-hole part:
http://www.mouser.com/ProductDetail/Vishay/TFPTL15L2200FL2B/?qs=sGAEpiMZZMvQRzVR7o8pIcPrhnnD25wXmlNEFnBMIZ0%3d
C.W.
everyone who's working with a prop-Chip or -board pays $10 before start experimentating.
The money will come back if the chip is still alive properly after finishing.
That's what would educate young people directly to responsible working by double-checking
if everything is wired right. It would be a very good preparation for the conditions in a real job
If somebody wants to "PLAY" give him the "playing-board (with current-limiting resistors on each-prop-pin with playing-LEDs)
If he wants to do the more interesting stuff pay for the chip and you will get it back if everything is still alive after finishing
best regards
Stefan