How to wire-up a flow sensor with Hall effect to operate a 12V relay

Thread Starter

bowsprit

Joined Oct 2, 2018
52
No, maybe very very little, No output when I stop water flow. Doubling the flow increases the volts, decreasing flow brings it back to around 5v
 

Ian0

Joined Aug 7, 2020
9,667
In the absence of a 16-pin LM2917, you could use two 555s, the first wired as a monostable to prevent the situation where the hall effect sensor stops in the LOW state.
Alternatively, an edge-triggered retriggerable monostable such as the 74HC123 would do the job. You would only need one, but they come in pairs! (and you already have the 5V supply)
 

Thread Starter

bowsprit

Joined Oct 2, 2018
52
That sound quite good. I wonder if you could come up with schematic for the 2 x 555 option.
If it makes it any easier for you , you could put it on paper, scan and attach here. Then I'll turn it into a project using Easyeda and publish the schematic & board in this forum for any corrections if needed.
 

Ian0

Joined Aug 7, 2020
9,667
That sound quite good. I wonder if you could come up with schematic for the 2 x 555 option.
If it makes it any easier for you , you could put it on paper, scan and attach here. Then I'll turn it into a project using Easyeda and publish the schematic & board in this forum for any corrections if needed.
Assuming 450 pulses per litre = 7.5Hz per litre per minute gives an alarm frequency of 90Hz, and a maximum frequency of about 300Hz.
First stage gives a negative-going 500us pulse for every output from the sensor, which discharges the 100nF capacitor.
It will the take 11ms for the 100nF to charge up to threshold level, and above that the output will be driven low and sound the buzzer.
The output can come from either pin 3 or pin 7. (Pin 7 is just an open-collector version of pin 3)
It’s pretty much a classic watchdog timer circuit.
Of course, the alarm will sound continuously if the engine is not running, so I’m presuming you will power it from the “ignition” circuit.
 

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Ian0

Joined Aug 7, 2020
9,667
Apologies for the quick scribble, but it’s 4.7nF. And if it‘s a good old fashioned full-fat 555, it will need 100nF from pin 5 to ground. The fancy new CMOS ones (ICM7555, TLC555) don’t, but you’d have to check that they have enough output current for the buzzer.
 

Ian0

Joined Aug 7, 2020
9,667
I'm assuming that the output is open collector (hence the 4.7k pullup), because the most common Hall-effect switches (Allegro, Diodes, Infineon, Texas and the high supply voltage Silicon Labs) are all 5V to 30V supply with open collector output. The Ebay listing doesn't specify the output.
 
Last edited:

sghioto

Joined Dec 31, 2017
5,378
I'm assuming that the output is open collector
Features:

  • Model: YF-S201
  • Sensor Type: Hall effect
  • Working Voltage: 5 to 18V DC (min tested working voltage 4.5V)
  • Max current draw: 15mA @ 5V
  • Output Type: 5V TTL
  • Working Flow Rate: 1 to 30 Liters/Minute
  • Working Temperature range: -25 to +80℃
  • Working Humidity Range: 35%-80% RH
  • Accuracy: ±10%
  • Maximum water pressure: 2.0 MPa
  • Output duty cycle: 50% +-10%
  • Output rise time: 0.04us
  • Output fall time: 0.18us
  • Flow rate pulse characteristics: Frequency (Hz) = 7.5 * Flow rate (L/min)
  • Pulses per Liter: 450
  • Durability: minimum 300,000 cycles
  • Cable length: 15cm
  • 1/2" nominal pipe connections, 0.78" outer diameter, 1/2" of thread
  • Size: 2.5" x 1.4" x 1.4"
SG
 

Ian0

Joined Aug 7, 2020
9,667
I'm still assuming that the output is open-collector. I found a photo of the internal workings, and you can see the pull-up resistor, which goes to the positive supply.
So with a 5V supply, it will be TTL compatible.
With a 12V supply, it will have a 12V output, so my circuit will work.
 

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Thread Starter

bowsprit

Joined Oct 2, 2018
52
There is no particular reason for the bridge, just trying things out. The sensor needs 12v to operate (5 to 18V).

I found the following maybe it's of any use:
1. Output pulse high level: >DC 4.5 V (input voltage DC 5 V)
2. Output pulse low level: 3. Accuracy: (flow-pulse output) within 2~120 L/min±1%
4. Output pulse duty cycle: 50±10%
5. Output rise time: 0.04μS
6. Output fall time: 0.18μS
7. Flow-pulse characteristics: horizontal test pulse frequency (Hz)=[0.45*Q]±2% (horizontal test) (Q is flow rate L/min)
 

sghioto

Joined Dec 31, 2017
5,378
I found the following maybe it's of any use:
Yeah those are some of the same specs I posted earlier but I don't believe those are accurate. If you are using a 12 volt supply then you should see 12 volts out when the magnet is not near the hall effect sensor.
Specs say: 4. Output pulse duty cycle: 50±10%
Seems like it would be more like the waveform below.
SG
EEE DN32 output.png
 
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