Sound Generator Design 2
15 May 09 - These sound generator chips have been discontinued and are no longer available. There appears to be no similar items available at present so an alternative (probably digital) solution will have to be developed.
This is a simple sound generator to produce jet engine aircraft sounds. It will run on any battery voltage between 3v and 40v. The current draw by the prototype was 100mA and it is recommended that the RX supply is used as this minimises the heat generated by the LM317MP.
The unit will produce 4 sounds that the manufacturer calls "low speed sound of aircraft", "high speed sound of aircraft", "missile" and "machine gun". They are activated by connecting pins 12, 13, 14 or 15 to ground respectively. I recorded 2 sound files whilst testing the unit - the first file (79k) is each of the four sounds in order. These were recorded with a fixed 430k resistance between pins 10 and 11. The second file (82k) is the low speed sound with manually changed resistor to increase then decrease the engine speed. The second file also has 2 bursts of machine gun fire overlaid at the maximum speed point. The machine gun and missile sounds can be triggered whilst the engine sounds are playing, they will continue until the switch is released and then the engine sound will resume. The speed of the tones increases with decreasing resistance between pins 10 and 11. This could be achieved if the variable resistor is connected to a servo (on the throttle channel). Unfortunately the speed of the machine gun & missile sounds is also dependant on the resistance and would fire slower at lower throttle settings.
Probably the most useful set-up is to permanently wire pin 12 to ground and put an RC switch between pin 15 and ground. This will give a constant engine note (once the unit it powered) and machine guns when the RC switch is triggered. An LED can be connected to pin 16 and will flash in time with the sound being played. It is probably of not much use except at night.
I have not actually built the Vero board design myself, but the construction is quite straight forward. Cut a piece of board to size and remove the tracks where indicated. I would recommend fitting a piece of insulation over the long pin of the 1uF capacitor as it bridges over a resistor. You don't need to fit the 50R resistor if you don't intend to fit the LED. The four optional switches indicated control the sounds produced. To produce the constant engine tone with machine gun blasts, fit a wire link instead of the switch nearest the potentiometer and a switch as indicated furthest from the potentiometer. In this case the middle 2 switches would not be required.
Fit the wire links, resistors, capacitors & LED (if wanted) and solder to the board. Solder the wiring pins & i.c. socket in position if you intend to use them. Fit and solder the ZTX302 and LM317MP in place. Solder the leads for the loud speaker, switch(es) and potentiometer to the board and components. Finally install the HT2844P, taking care not to damage it with static electricity (touch some bare metal on a central heating radiator or water tap prior to removal from the protective packaging. Apply power & test.
I will experimenting with ways to remove the requirement for a servo and to use the PWM signal from the RX direct.
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