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counter_struck
03-25-2008, 01:04 AM
Hi

I am designing a ultrasonic range finder.

I found some circuits avaliable on the net. There is a section on the transmitter circuitry that confuses me. I am using microcontroller to generate a 0 - 5V 40KHz burst of pulses. I want to boost the signal to have a larger voltage swing, and current drive to achieve larger power transmission hence further distance. I can amplify the voltage to 0 - 9V, but now how do I achieve a -9V to 9V swing?

The circuit uses hex inverters. Doesn't a hex inverter represent a logic 0 as ground? The explanation given about why two hex inverters are in parallel is still not clear to me.

http://www.interq.or.jp/japan/se-inoue/e_sonic1_3.htm
(Ultrasonic drive circuit)

I am using a PIC microcontroller, which drives out about 20mA. I want to achieve the max power transmission for a 40KHz piezo transducer. For current amplification, how does one design this for a -9V to 9V signal?

elecrom
03-26-2008, 02:59 PM
Simple ... use MAX232 ... it generates +-9V ... give complimentary uC outputs to (T1IN,T2IN) inputs of MAX232 and connect its outputs (R1OUT, R2OUT) to transmitter. You will nicely get +-9V swing.

By the way, it is always better to improve sensitivity of receiver than increasing transmitter power.