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Step 4The Controller
I built the controller in a plastic box I picked up for much too high a price at Fry's electronics. You can use almost anything as long as it is big enough. This box was designed for a 9V battery but I needed to use 6V so the battery space is wasted. I could have easily fit the circuit board in the 9V battery compartment.
Whatever box and switches you use, plan the layout and make sure everything will fit together when you try to close it up.
Note that there is a diode connected in series with the battery. It is there to bring the supply voltage down to an acceptable level for the uC which is rated for 5.5V maximum Vcc. Even with the diode, the part is running at the limit with fresh batteries so don't get any fancy ideas about running at 9V unless you add a 5V regulator. I toyed with the idea of using a PIC12HV615 instead because it has a built-in shunt regulator, but the swing between minimum and maximum currents are too much for the shunt regulator so I'd have to complicate the circuit a bit to get it to work. I wanted to keep this really simple, mostly because I'm lazy but also because I have other projects going and I wanted to finish this one ASAP.
The relay I used has a built-in protection diode shown but not labeled on the schematic. The diode protects the uC from the inductive reverse voltage kick that occurs when you fire a pulse into an inductor like a relay coil. If you use a different relay be sure to add a diode with the polarity shown or maybe you can kiss your uC goodbye the first time the relay fires. The uC can safely sink about 25 mA from one pin so choose a relay with a high resistance coil. The PRMA1A05 has a 500 Ohm coil so it only takes 10-12 mA to close it.
I wanted to use some nice thin, light cables with RJ-11 connectors but all the connectors I found at Fry's were PCB mount parts so I ended up going old-school with DB9s. Serial cables are dirt cheap and the screws will keep the connectors from falling out. You really only need to connect 3 wires (Vcc, Gnd, and the combined outputs of the two IS471FEs) between the optical assembly and the controller so you can use almost any connector/cable you like, even a stereo mini plug and jack.
Whatever box and switches you use, plan the layout and make sure everything will fit together when you try to close it up.
Note that there is a diode connected in series with the battery. It is there to bring the supply voltage down to an acceptable level for the uC which is rated for 5.5V maximum Vcc. Even with the diode, the part is running at the limit with fresh batteries so don't get any fancy ideas about running at 9V unless you add a 5V regulator. I toyed with the idea of using a PIC12HV615 instead because it has a built-in shunt regulator, but the swing between minimum and maximum currents are too much for the shunt regulator so I'd have to complicate the circuit a bit to get it to work. I wanted to keep this really simple, mostly because I'm lazy but also because I have other projects going and I wanted to finish this one ASAP.
The relay I used has a built-in protection diode shown but not labeled on the schematic. The diode protects the uC from the inductive reverse voltage kick that occurs when you fire a pulse into an inductor like a relay coil. If you use a different relay be sure to add a diode with the polarity shown or maybe you can kiss your uC goodbye the first time the relay fires. The uC can safely sink about 25 mA from one pin so choose a relay with a high resistance coil. The PRMA1A05 has a 500 Ohm coil so it only takes 10-12 mA to close it.
I wanted to use some nice thin, light cables with RJ-11 connectors but all the connectors I found at Fry's were PCB mount parts so I ended up going old-school with DB9s. Serial cables are dirt cheap and the screws will keep the connectors from falling out. You really only need to connect 3 wires (Vcc, Gnd, and the combined outputs of the two IS471FEs) between the optical assembly and the controller so you can use almost any connector/cable you like, even a stereo mini plug and jack.
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