Pico Technology

Figure 1 Set up of PicoScope 2202, pulse generator, coaxial cables and computer

Equipment

• PicoScope 2202 PC Oscilloscope^#1
• USB cable (supplied with the PicoScope 2202)
• PicoScope software (supplied with the PicoScope 2202)
• Computer, monitor, keyboard, mouse, etc
• 2x cable BNC plug to BNC plug 16-0330 (Rapid)^#2
• 100 m  50Ω impedance RG58C/U coaxial cable 02-0220 (Rapid)
• 200 m  75Ω impedance RG59B/U coaxial cable CAB59 20 (Connectorco)
• 5x standard coaxial plugs 16-0400 (Rapid)
• 2x coaxial coupler 16-0417 (Rapid)
• Pulse generator (see construction details)

^{#1 Alternatively a Pico ADC-200 and parallel port cable can be used.
#2 Change one of these cables to BNC plug to coaxial plug.}

Components required for pulse generator

• Stripboard 0.1" matrix with copper one side only 34-0505 (Rapid)
• 2x 1.2 kΩ  0.6 W resistor 62-7734 (Rapid)
• 4.7 kΩ  0.6 W resistor 62-7764 (Rapid)
• 47 kΩ  0.6 W resistor 62-7812 (Rapid)
• 2x 220 pF capacitor 08-0525 (Rapid)
• 2x 2N3904 transistor 81-0484 (Rapid)
• 2x 1N4001 diode 47-3130 (Rapid)
• 2x BNC bulkhead mount socket 16-0110 (Rapid)
• Switch SPST subminiature toggle 75-0100 (Rapid)
• Battery clip for PP3 battery 18-0093 (Rapid)
• Diecast aluminium box 30-1532 (Rapid)
• Reel orange connecting wire 01-0325 (Rapid)
• Reel black connecting wire 01-0305 (Rapid)
• Reel red connecting wire 01-0335 (Rapid)
• Alkaline PP3 battery 18-4230 (Rapid)
• Solder
• Access to soldering iron, drills, pliers, saw and file

Construction details

Terminate each end of the coaxial cables with coaxial plugs. Label the 100 m cable A with a speed of 2.10 x 10⁸ ms^-1 and the 200 m cable B with a speed of 1.90 x 10⁸ ms^-1.

Remove one of the BNC plugs from the end of just one of the BNC plug to BNC plug cables and replace it with a standard coaxial plug.

Figure 2 Matrix board layout and associated circuit diagram

Figure 3 Inside of diecast box

Figure 4 Top of diecast box

Saw a piece of stripboard 12 strips x 17 holes as shown on the matrix board layout in Figure 2. Make the cuts in the board as indicated and then mount the components as shown together with the various connecting wires and the black lead of the 9 V battery connector. Note carefully which way round the diodes and transistors need to be mounted. Most faults in circuits occur when tiny solder links cross between the rows of copper, so check with a magnifying glass that such links have not been produced.

Stick a few strips of pvc insulating tape to the base of the diecast box where the stripboard is to be placed. This will prevent any shorting of the stripboard components by the aluminium of the box. Mount the BNC sockets and switch on the diecast box as shown in Figure 3, place the matrix board inside the box and link the orange connecting wires to the BNC sockets, the red connecting wire to the switch, and the red lead of the 9 V battery connector also to the switch. Label the top of the diecast box as shown in Figure 4.

Testing the pulse generator

Connect the pulse generator’s BNC socket labelled Pico to Channel A of the PicoScope 2202 or ADC-200. Connect a USB lead from PicoScope 2202 to a USB socket on the computer. (If you are uisng an ADC-200: connect the parallel port lead from the ADC-200 socket to the parallel port socket on the computer. Plug in the ADC200’s power supply.)

Switch ON the computer and load the PicoScope software. Enlarge, if necessary, to provide a full screen display as shown in Figure 5 below with the program already running.

Figure 5 PicoScope initial screen display

Click the red STOP button in the bottom left-hand corner of the screen. Adjust the Timebase setting to 5 µs/div; the X-gain to x1; Channel A to ±1 V, AC and Y-gain of x1. Leave Channel B off. Now set the Trigger to Single, (channel) A, Rising and 5 mV, and the Pre-trigger screen display to -5%. The last of these lets you set when the trace is started from, in this case the first 5% of the display is prior to the pulse triggering.

Switch ON the pulse generator and click the green GO button in the bottom left-hand corner of the screen. Figure 6 shows a typical output trace.

Figure 6 Typical output trace from pulse generator

Now close down the Oscilloscope screen. Click on the Frequency meter icon and select ch A, Frequency, Auto and AC in the Toolbar, and reset the Trigger to Auto but leave all the other settings as they were. Click on the green GO button You should get the screen displayed as in Figure 7 with the frequency of the pulses showing near 140 kHz. My pulse generator showed 137.4 kHz which is good enough.

Figure 7 Frequency meter display

To finish with the program click on File in the Menu bar and then Exit in its drop-down menu. Do not forget to switch OFF the pulse generator if it is finished with at this stage and disconnect the cables.

Suppliers

Tel: 01276 405320
Fax: 01276 405329
E-mail: sales@connectorco.com
Web: www.connectorco.com

Tel: 01480 396395
Fax: 01480 396296
E-mail: sales@picotech.com
Web: www.picotech.com

Tel: 01206 751166
Fax: 01206 751188
E-mail: sales@rapidelec.co.uk
Web: www.rapidonline.com

• Experiment
• Teacher’s notes
• Technician’s guide