Single 3.3V Inverter

[flippineck]

Looking for a single channel inverter that will take as a square wave input, a 0V level which rises to 3.3V for one second and then drops back to 0V, and convert it to a 3.3V square wave output which falls from an initial constant 3.3V, to 0V for one second before rising back to 3.3V

The input comes from the centre of a 4k7/10k voltage divider across the wider circuit's 5.0V supply rail, switched on the positive side of the resistors by an NPN transistor.

If necessary I could power the inverter in some manner from the wider circuit's 5.0V supply rail.

It should be as simple & cheap as possible and consume as little power as possible, whether composed of discrete components, or an IC. I'd like to avoid using a large chip with loads of redundant inputs, just seems wasteful?

This is to condition a control signal feeding into the 'Addkey 1' input of a 'DFPlayer Mini' mp3 player module.

Could a 741 op-amp be a good solution? My signal's not actually electrically inverting though is it.. it's only a logic state inversion.. head's about to burst :-(

 

[bertus]

Hello,

Is the pulse already made and only needs to be inverted?
Have a look in the pocket databook:
https://www.ti.com/lit/ug/scyd013b/scyd013b.pdf
Page 92 shows a small inverter chip.

Bertus

 

[AnalogKid]

The mere mention of a 741 will bring down a plague of locusts from some members. their "passion" not withstanding, they are correct in this case. A 741 will not perform this function with the power sources you have available.

This will: One NPN transistor as an inverting saturated switch, with one pull-up resistor on the collector to the 3.3 V rail. No additional base resistors needed because the two that form the input signal are perfect for this.

ak

 

[flippineck]

As the setup stands (it's a timer board from China), there's no actual 3.3V rail as such. The board provides a good stable 5.0V from a small buck chip. At the moment I have it connected to a 9V pp3 battery, in the application I have planned, it'll be 4 x D cells giving 6V.

As supplied the board does some unknown magic in a hidden region underneath a big 4 digit LED, which results in an output signal snaking out on a thin track from under the LED and onto the NPN transistor's base. Originally the emitter of the transistor went to ground, and the collector fed a relay. The transistor allowed the current from buck chip's 5V through the relay, through the EC junction, and on to ground. Idea was, you would then control your things directly off the relay contacts.

I've removed the relay which was taking too much current for my application when powered continuously for hours, and replaced it's 70 ohm coil in the NPN's + leg (collector) with the 4k7/10k voltage divider in it's - leg (emitter). The hope is, I can now read something close to a 3.3V/0V signal directly off the centre of the divider whilst keeping current low and not killing a small battery in a day.

Now if I want to invert this signal (hopefully so I can use it to trigger a DFPlayer mp3 player module to do a one-shot play of segment 1 i.e. the first mp3 on the SD card), I should be able to use the transistor arrangement you describe above, by giving it it's own 3.3V feed from a second, dedicated 4k7/10k voltage divider across the timer board's 5.0V buck chip supply?

Would a BC548 be ok here?

 

[flippineck]

Sorry to double post, too late to edit. Just occurred to me I could just replace the relay coil with the 4k7 resistor, connect the 10k resistor from the J3Y (existing NPN on the board) collector to ground, and take the 3.3V / 0V signal straight off the J3Y's collector. It should then be unnecessary to invert the pulse? Direct line of thinking on from AnalogKid's post.

This would also have the beauty of not disabling the indicator LED on the timer board, which seems to rely on the J3Y's emitter going straight to ground and not through a large resistance.

 

[AnalogKid]

Could work. Post a schematic to be sure.

ak

 

[flippineck]

Sorry, I know, I really must find a better way of doing diagrams