Run a piezo sounder and an LED from a TTL output?

[Chris Wilson]

I have a miniature receiver that has 4 TTL outputs, each independently triggered by 4 channels from a paired transmitter. Each output is TTL and rests low, and is driven high.

I want each TTL output, when set high by the corresponding channel on the TX being heard, to both light an LED and sound a 3V 40mA piezo sounder. One sounder and one LED is dedicated to each TTL RX output. The receiver and transmitter both run on 2 to 3.6V at minimal current. I have a mains powered 3.3V step down supply at 5W for the TX and another for the RX. It would be ideal to use the same supply to drive the piezo sounder and an LED per channel for the receiver.

I am thinking MOSFET to do this but would need a basic schematic  with values and a comfortably excessively rated MOSFET part number.

A concern is sharing the RX supply with whatever the TTL outputs drive.

Here is a link to the datasheet for the RX and TX devices:  https://www.rfsolutions.co.uk/downloads/62822381d8de6982DS-ZPT-3.pdf

Would anyone be kind enough to help me here please?

Thanks.

[jonpaul]

ttl open collector driver IC

search TI.com

jon

[Zero999]

Does the piezo have a built-in oscillator?

[DavidAlfa]

Piezo drivers are basically capacitors.You need to drive them hard to make the sound.
Volume will be pretty low using a weak driver like a TTL outputs.
If they have built-in driver,then it might work, but still 20mA typical per TTL output it's too low.
Perhaps parelleling several outputs, but why? Just interface a small transistor.

[pcprogrammer]

The output drive capability of these modules is only 5mA at 3.6V supply, so yes you would need a transistor to beef things up. A 2n7000 can drive up to 400mA and gate on threshold is typically 2.1V.

Links to data sheet and some explanation about using a mosfet as a switch.

https://www.onsemi.com/pdf/datasheet/nds7002a-d.pdf
https://www.electronics-tutorials.ws/transistor/tran_7.html

To get the piezo sounder to work you might need an oscillator to drive it. Depends on the type you plan to use.

https://www.circuitbasics.com/how-to-use-active-and-passive-buzzers-on-the-arduino/

[Zero999]

A 2n7000 can drive up to 400mA and gate on threshold is typically 2.1V.

The data sheet says 115mA continuous. The gate threshold voltage is only specified at 250µA.  The 2N7002 is specified at V_GS = 5V & I_D = 50mA. You might get away with a gate voltage of 3.6V and a drain current of 40mA, but it's marginal.

There are MOSFETs which should pass 100mA or so with a gate voltage of just 3V. I found the NX3008NBK and PJA138K, in Mouser.
https://www.mouser.co.uk/datasheet/2/916/NX3008NBK-1545540.pdf
https://www.mouser.co.uk/datasheet/2/1057/PJA138K-AU-1867157.pdf

[DavidAlfa]

But a piezo doesn't draw continuous power, it's all peaks, like a cap. So the average could be 10mA, with much higher peak currents.
You can get it done very easy:
https://www.edn.com/increase-piezoelectric-transducer-acoustic-output-with-a-simple-circuit/