Have you ever wanted to tell your dog to stop barking without having to yell? Does your neighbour have a dog that just won't be quiet? Use an electronic dog whistle to produce an ultrasonic noise between 11 and 22 kilohertz, or kHz, that will be loud and clear to the dog, but inaudible (or nearly so) to you and your human neighbours. In the simple circuit described below, a 555 timer, a potentiometer and a piezometer act together to produce variable frequency sound.
- Skill level:
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Things you need
- NE555 timer
- 9-volt battery
- Piezometer, 82 decibel
- Potentiometer, 4700 ohm
- Resistor, 4700 ohm
- Resistor, 1200 ohm
- Capacitor, 10 microfarad
- Capacitor, 10 nanofarad
- Electrical wire, 22 gauge
- Soldering iron
- Perfboard, 4 inches by 4 inches
Set your 555 timer in the perfboard. This is what you will be soldering the rest of the circuit around, so it makes sense to place it first. The perfboard is a simple piece of flat plastic with lots of small holes so that you can arrange and contain the circuit on a flat surface.
Solder a wire lead off each of the positive and negative battery terminals. Connect the positive lead to one lead of the switch. Solder the other lead of the switch to the 4700-ohm resistor.
Connect the other 4700-ohm resistor lead to output #7 (labelled "DIS") on your 555 timer. The 555 timer outputs will be labelled either by number or by shorthand name, such as "DIS." Continue the electrical path by soldering another wire between output #7 and the 1200-ohm resistor.
Attach the other side of the 1200-ohm resistor to the centre lead (of three) on the potentiometer. A potentiometer is a variable resistor; for this circuit it allows you to control the frequency (in kilohertz) of the output sound. Leave one of the remaining potentiometer leads free. Use a length of wire to solder the last lead to outputs #2 (TRIG) and #6 (THRE) on the 555 timer.
Solder one of the leads of the 10-nanofarad capacitor to the wire that you just connected between the potentiometer and the 555 timer. Make sure to remove the insulation of the wire so that you are soldering metal to metal. Use wire to connect the opposite lead of this capacitor to output #1 (ground) on the 555 timer, as well as to the negative output of the piezometer. Then solder the negative lead of the piezometer to the negative terminal of the battery.
Join the positive lead of the piezometer to the 10-microfarad capacitor and continue this electrical path by connecting the opposite lead of the capacitor to output #3 (OUT) on the 555 timer.
Solder a wire between 555 timer output #8 (VCC) and the wire connecting the switch to the 4700-ohm resistor. Do the same between output #4 (RSET) and the wire between the switch and the resistor. Only output #5 (CONT) should be left free on your 555 timer.
Test your circuitry by pressing the switch "on" and turning the knob on the potentiometer to adjust the frequency. Humans can generally hear within a range or 20 hertz to 20 kilohertz, so you should be able to hear the piezometer making sound during part of the potentiometer's range. If the circuit is not working, check all of your solder connections, as well as your battery.
Tips and warnings
- Test your electronic dog whistle at various frequencies (by adjusting the knob on the potentiometer) to determine what your pet responds best to.
- Never solder with your power source "on." For this circuit, you should be aware of where your switch is to make sure that it is not accidentally pressed "on."
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