Sound Generator Design
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 that 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.
I've recorded the unit whilst testing it and manually operated a variable resistor to change the engine speed - Hear it Roar (132k).
When the switch connected to pin 4 is open the HT2812A is in standby mode. The a switch can be removed and pin 4 connected to pin 9 (negative rail) but sound would be produced when power is attached.
The frequency of the tone (engine speed) increases with decreasing resistance between pins 5 and 6. If the 270k variable resistor is connected to a servo (on the throttle channel) the engine speed will automatically be adjusted in flight.
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 to prevent it touching the pins of the HT2812A. Fit the wire links, resistors and capacitors 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 and potentiometer to the board and components. Finally install the HT2812A, 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 be experimenting with ways to remove the requirement for a servo and to use the PWM signal from the RX direct.
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