Connecting a flow sensor requiering pull up to a LLC

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Mikael77

Joined May 24, 2019
1
Hi

I want to connect a flow sensor (SF800) to a ESP12, since the ESP is running on 3.3v and the sensor needs 5V I need a logic level converter. I'm using one that uses pull up's and a mosfet (LLC.png).

On its HV (5V) end it has a 10k pull up resistor. According to the specs of my sensor it needs a 2200 pull up resistor (SF800-data.png).

The combined circuit would have a 10k and a 2200 resistors in parallel (R2 & R3 ESP-Flow-Dia.png), which I assume would not work.
Any suggestion on how the sensor can be connected, preferable using the same LLC?
 

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Alec_t

Joined Sep 17, 2013
10,470
Welcome to AAC!
The LLC seems rather elaborate. Depending on the source input impedance requirements of the ESP, would this simpler arrangement suffice? It limits the ESP input to ~ 3.1V.
LLC.PNG
This could be simplified further (at the expense of a higher standby current) by eliminating R1 and making R2=3k9.
 

dendad

Joined Feb 20, 2016
3,084
If the outputs are open collector, no level conversion is needed. Just connect the pullups to 3.3V.
Try running it and see if there are pulses coming out with no pullups. Then if not, connect the resistors to 3.3V and see if that works ok.
But I think they will be open collector as that is a usual way these things are made, to allow connection to various voltage rated inputs.
 
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