# Trying to figure out what battery I need

Precursor: I'm really new to electrical engineering. My background is in software. I'm trying to learn but having a difficult time. (Any recommended reading/books is appreciated). At this point, you should probably assume that I know nothing.

I'm trying to use Massa's TR-89 ultrasonic transducer to produce a 40 KHz frequency. I am testing this on both an Arduino Pro Mini and Espruino Puck.js.

The whole volts, amps, watts stuff confuses me. I need to use a lithium ion rechargeable battery, and I want to make sure that the 40 KHz frequency reaches up to 50 ft (as it's suppose to).

It's my understanding that I would need to use a PWM pin and a transistor in order to (I think) switch the current (don't have a good grasp on this) coming from the battery which, in theory, has a larger voltage that what the Arduino/Puck.js can output. I also want to make sure that I don't supply the arduino or puck.js too much voltage.

Am I on the right track here?

Transducer datasheet:

the 40 KHz frequency reaches up to 50 ft

What you mean by "reaches"?

You need an ultrasonic driver circuit that can produce a square wave of 12-35V or sine wave 12-45V, the higher the better, up to the maximum permitted according to the data sheet. It is not really a function of the battery.

Google "ultrasonic driver circuit" and click on "images" for many examples.

you could use multiple 18650 cells in series. They are rechargeable and comes in capacities up to ~3300mAh per cell.

For figuring out the battery you need to know the power consumption and endurance required, and the
desired voltage (12V is convenient for a 12V circuit, 5V for a 5V circuit).

To know that you need to know the power consumed by each part of the circuit (well the most power
hungry bits are the one's to worry about).

To drive the transducer you'll need a suitable circuit that's matched to the power and impedance of
your transducer, typically(*) I've seen resonant transformer outputs used driven from a 5V square wave
on the primary, which means either learning about analog signal handling or finding a suitable circuit
someone else has designed.

The example transmit circuit they show in the datasheet is limited to 15V square so won't give maximum
range, but at least it is simple.

To receive you need some analog amplification and band-pass filtering, and also a circuit to protect
the receive amplifier from damage during the transmit pulse.

If range is important to you as you imply, don't use the 40kHz transducer, use the 23kHz transducer, it
has more range.

(*) ie the circuit used in cheap car-reversing sensor unit from eBay.