Screamer

A few years ago, I went to a workshop sponsored by Science World here in Vancouver. One of the projects we made was a Drawdio pencil...

https://makezine.com/projects/drawdio-musical-penc...

https://www.instructables.com/Drawdio/

Recently, I stumbled on all the parts from way back when and remembered how fun it was. However, I wanted something without the pencil.

• TLC555
• 10 Ω resistor
• 10 KΩ resistor
• 270 KΩ resistor
• 10 MΩ resistor
• 0.1 uF capacitor
• 570 pF capacitor
• 100 uF electrolytic capacitor
• 8 Ω (0.25 W or 0.5 W) speaker
• 2×AA battery holder
• 2N3906 tansistor
• 8-pin IC holder (optional)
• 3cm × 7cm breadboard (or perf board)
• switch (optional)
• wire

Place the TLC555 on a breadboard and connect...

Pin 1 -- GND

Pin 2 -- Pin 6; 270KΩ to Jumper 1; 570pF to GND; 10MΩ to GND

Pin 3 -- 2N3906 Base

Pin 4 -- Vcc

Pin 5 -- 0.1uF to GND

Pin 6 -- (see Pin 2 above)

Pin 7 -- Jumper 2; 10KΩ to Vcc

Pin 8 -- Vcc

2N3906 Emitter -- Vcc

2N3906 Collector -- 100uF to SPKR+ to GND; 10Ω to GND

2×AA Battery + Lead -- Switch to Vcc

2×AA Battery - Lead -- GND

Once the complete circuit has been tested (and works) on the breadboard, it is time to solder things in place.

I used a 3cm × 7cm, double-sided, PCB prototype board. You may be able to design a more efficient layout than this, and you may want to use a different-sized board. This worked well for the speaker I had.

The solid lines in the diagram are jumper wires on the top side of the PCB. The dashed lines are connections on the back side of the PCB, usually made by bending the leads of one of the components. For example, the bottom lead of the 10M resister was soldered to Pin 2 and then bent to be soldered to Pin 6. The top lead of the 270K resister connects to Pin 6 as well. The top lead of the 10 Ohm resister was soldered to Pin 1.

I 3D printed a case to protect the connections on the back of the PCB and to facilitate the attachment of the battery holder. You could easily use AAA batteries as well.

I ran the wires from the battery pack through the holes in the case and through the top screw holes in the PCB.

I attached terminal connectors to the ends of the jumpers after I ran the jumpers (orange wires) under the PCB and out the bottom screw holes of the PCB. (Note: Because I ran the jumpers under the PCB, they are not visible in the pictures. They pop up through holes D8 and I8 on the PCB -- you can just barely see them -- before dropping back down D7 and I7 to be soldered.)

I used some double-sided adhesive tape to secure the PCB and the battery holder to the case.

The TLC555CP that I used is rated (if I am reading the data sheet correctly) from 2V to 15V. With two AA or two AAA you will get somewhere under 3V. This is plenty loud enough. Based on other projects I have done with the TLC555CP (though I did not try it with this one), the higher the voltage, the louder the volume.

The Screamer can be used as a rudimentary Ohmmeter. The higher the pitch, the lower the resistance between the jumpers.

Try having one person hold one jumper while another person hold the other jumper. You should be able to activate the Screamer by holding hands or touching fingertips.

Graphite -- found in pencils -- is a resister. If you trace a pencil line on a piece of paper, touching the jumpers at varying distances apart from each other along that line should produce different tones. It may even be possible to create a graphite piano.