Hardware Reference
In-Depth Information
Next up, install the five capacitors. It won't matter what sort of capacitor you use as long as it has the correct
value of 0.1 mf. Where did I get a value of 0.1 mf? If you are asking this, then I know you have not read the data sheet.
Inside the data sheet there is a table of input voltages and their matching capacitors. Because the Raspberry Pi is
3.3 V I should use 0.1-mf capacitors according to the data sheet. Capacitors can be polarized or nonpolarized. I use
nonpolarized capacitors but if you use polarized capacitors make sure you install them in the correct orientation.
1.
Start off by installing the charge pump capacitors across pin 1 and pin 3 of the IC; then
place another capacitor across pin 4 and pin 5.
2.
Install the 5.5-V negative and positive charge pumps. Install a capacitor from pin 2 to a
spare row. I'll take this to the side of the IC. Do the same for pin 6 as well.
3.
Lastly install a capacitor between pins 15 and 16. This will ensure you have a stable voltage
input similar to the C6 capacitor on the Raspberry Pi. You can see the installed capacitors
in Figure
9-5
.
Figure 9-5.
The installed capacitors
Now you can install the wire links.
1.
Connect pin 15 to the ground rail via a jumper cable. Then connect pin 16 to the positive rail.
2.
Connect the free leg of the capacitor from pin 2 to the ground rail.
3.
Lastly install a jumper cable from the free pin of the capacitor from pin 6 to ground as well.
This is why you install the pair of jumper wires between the two sides of the power rails: it
makes wiring the MAX3232 a lot easier.
Before you connect the MAX3232 to the Raspberry Pi, I want you to check the potential voltage on this circuit.
At this point there should be no connection to the Raspberry Pi.
1.
Connect an external 3.3-V source to the board's positive rail and the ground rail to the
ground of your external source. There is no need to make this a permanent connection.
2.
Power on the circuit.
