There is a slight problem with driving an IN-9 with the Arduinix :
- first, the voltage is too high (I am using IN-8 in a mulitplexed fashion as per their datasheet that states 200V, 10%, 1 to 2ms spikes).
- second, all the PWM ports are taken by the ArduiNIX.
- third, even if you could connect a PWM port, the PWM frequency is too low for the IN-9 to function properly.
After browsing the web, and discarding solutions that involved the use of a DAC, I came up with my own simple solution though.
Here is the schematic:
+200V +
|
Z
Z 8.8Kohms/1W (see note)
Z
|
(˚) IN-9
T
|
+ collector
\|__________+____ base (PWM, port 10)
/| MPSA42 |
| emitter |
| === 10µF
| |
+-----------+
|
Z
Z 330 ohms
Z
|
_+_ GroundThe 10µF dampens the 400 or so kHz from the Arduino enough that the MPS42 sees it as a DC voltage
For the 1W resistor, since I don't have that in my drawer, I used 4 2.2K 1/4W resistors. Each resistor takes 1/4 of the voltage drop. They get warm to the touch, but at least they won't fry. The current is 10mA for the maximum range, and the voltage drop around 100V.
This disables usage for the 4th anode of the ArduiNIX (port 10). If you have one anode left, you can use it.
Since I am using all three anodes left in my design (long story short, don't buy 7441s, use 74141s instead), I took the high voltage from the test point on the ArduiNIX board.
Video in action at
http://www.youtube.com/watch?v=MUf1HjGagWcIf anybody has a better idea to produce the lower voltage required, I am interested...
Philippe
