I’ve had a couple of questions asking about using capacitors to fade out the LEDs of the spindicator to give a sort of trail effect, and I thought I’d like to try it myself. So let’s get straight to the circuit.
The first thing to note is that in this version I have used the computers 12V supply, not the 5V supply as in the original spindicator. This is necessary to obtain a good fade effect from the capacitor.
The motherboard interface and low pass filter are the same as in the original circuit. The difference is that the counter’s outputs now switch general purpose NPN transistors (a BC 547 in this case). When a transistor switches on, its associated LED is lit via the 1k Ohm resistor, and the 47uF electrolytic capacitor charges. When the transistor switches off, the capacitor discharges via the 1k Ohm resistor and LED, fading the LED as the charge dissipates. The fade time is a function of the values of the resistor and capacitor; the larger the values the slower the fade. The resistor is also the current limiting resistor for the LED, so that sets a limit to its value (between 470-1000 Ohms for most LEDs). What I found with breadboard testing is that if the fade time is too long, the whole spindicator ring lights when there is lots of disk activity, and you lose the spinning effect. I found that a 47uF capacitor gave a noticeable but suitably quick fade to each LED.
A challenge I faced with this circuit is that it has many more components than the original spindicator, with an extra 10 capacitors, 10 transistors and 20 resistors. The prototype board and patch wires approach would be too big and messy, so I decided to make my own PCB. With some trial and error I managed to get a reasonable result by laser printing (Brother HL-2170W) a design onto some Canon glossy photo paper (GP-401) and using an iron on its hottest setting to transfer the toner to a blank copper circuit board. It required some hard pressing to stick the print to the board, and then more working over the areas where the traces were with the tip of the iron. What I found though is that the paper then pulled away cleanly, leaving the traces stuck to the board. There was no mucking around soaking off the paper in water as others have reported when using this technique. If some of the traces pull off with the paper, you can just clean the board with some xylene based brush cleaner and try again with a fresh printout.
The above photo shows my copper board with its toner transfer sitting in the ammonium persulphate etching solution. You’ll notice some rough edges on the left hand ground trace, but there was enough cover left so I didn’t bother to print it again.
The end result, with components all soldered in is shown in the photo at the beginning of this post. I’ve connected all the LED cathodes together (not shown) so that there is only one common cathode wire and 10 anode wires running to the LEDs. I have not yet installed this spindicator – I’m waiting for the next time I’m doing some work inside the server (probably when I upgrade to WHS 2011).
Here’s a quick video of the spindicator mk.2 working at a constant clock frequency of about 25 Hz. The background sound in the video is rain on my workshop roof.