The MagPi - July 2018

Tutorial

raspberrypi.org/magpi July 2018 47

Voltage

Voltage A3

5V

Gnd

Time A2

Trigger A4

10K

10K 10K Time

Trigger

STEP-03
Wiring the pots

We then drilled three holes for the pots, and

added the small slots for the anti-rotation lugs.

Then we fitted the pots and wired them up using

the diagram above. This is the view from inside the

lid of the box; if you're worried about touching the

side of the box with your soldering iron, consider

soldering them before attaching to the box.

the information as to whether to use a trigger or not

on the next sample.

Finally, before each buffer full of data is gathered,

pin 13 on the board is lit, and turned off after. This is

so that we could time the process on a commercial

oscilloscope to find the sample rate – something you

will not have to do if you use the recommended AVR-

type Arduinos running at 16MHz.

Pi software

The software for the Raspberry Pi is written in

Python 3 and used the Pygame framework. It proved

to be a lot more tricky to write than we first imagined,

and is shown in the Scope.py listing. Python 3 uses

Unicode characters by default, and allowed us to

display the delta (Δ) and mu (μ) Greek characters for

the difference and the time. The code first sets up the

non-display part of the window, this is only drawn

once and then parts of it are updated when necessary.

Depending on what type of Arduino you have, it can

show up as a different USB port; we found that ours

>STEP-04

Finishing off

Add the resistors and capacitors to the

stripboard and wire up the BNC socket. Solder

this up before mounting, otherwise you will

melt the plastic. Remember to thread the

central wire through the ground washer,

crinkle washer, and nut before soldering

it. Add labels Trigger, Time, and Volts to

the knobs.

BUILD AN OSCILLOSCOPE