Run a piezo sounder and an LED from a TTL output? - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: November 21, 2022, 09:30:57 pm
content: 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.pdfWould anyone be kind enough to help me here please?Thanks.

author: jonpaul
author_rank: Super Contributor
timestamp: November 21, 2022, 09:40:45 pm
content: ttl open collector driver ICsearch TI.comjon

author: Zero999
author_rank: Super Contributor
timestamp: November 21, 2022, 10:28:27 pm
content: Does the piezo have a built-in oscillator?

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 21, 2022, 10:37:53 pm
content: 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.

author: pcprogrammer
author_rank: Super Contributor
timestamp: November 22, 2022, 05:46:31 am
content: 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.pdfhttps://www.electronics-tutorials.ws/transistor/tran_7.htmlTo 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/

author: Zero999
author_rank: Super Contributor
timestamp: November 22, 2022, 09:01:17 am
content: Quote from: pcprogrammer on November 22, 2022, 05:46:31 amThe data sheet says 115mA continuous. The gate threshold voltage is only specified at 250µA. The 2N7002 is specified at VGS= 5V & ID= 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.pdfhttps://www.mouser.co.uk/datasheet/2/1057/PJA138K-AU-1867157.pdf

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 22, 2022, 09:50:03 pm
content: 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/