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I am working on a autonomous track vehicle. I have mounted

3 HC-SR04 sensors 1 Sharp infrared distance sensor 3 infrared led distance sensors

1 Arduino Mega 2560 1 H-bridge Board HG7881

I am trying to use 7.5 v 1700 mAh Nicd battery (also tried 11.1 Lipo 2200 mAh) For all sensors power (5v) I developed 5v regulator using 7805 which is connected directly from battery as input. The output 5v is going to power distribution board (used from quadcopter extra board) which provides 5v to every sensor.

The real problem starts here when I am not getting correct or nothing in reading from Ultrasonic sensors and my vehicle starts behaving abnormal. I checked that sensor reading is either 0 or wrong. I used both simple and with NewPing library.

I checked when using 7.2v battery the output from 5v regulator is 3.72v.

Now my question is if the power is below 5v, does sensors starts behaving like this? How can we supply voltage so every sensor will receive full 5v to work properly?

My vehicle will not work until sensors provide correct distance reading. I worked successfully with one sensor but with number of these, tired working since many days.

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    The sensors are 5V so yes, very likely they will behave erratic at 3.7v. Have you measured the current draw from the battery while everything is running? Do you have input/output capacitors? Any thin/long wire being used? All connections are ok? Does any part gets hot? Not a problem but a switching regulator might be more efficient. – Talk2 Jun 29 '16 at 3:49
  • What's the voltage into the regulator? – Dave X Jun 29 '16 at 4:36
  • How is the Arduino wired into the sensor schematic? – Majenko Jun 29 '16 at 8:59
  • @Talk2, yes 5v sensors, should I check drawing current from battery by multi-meter just touching +v -v?, yes several thin but strong long wires being used. Yes checked connections to every sensor by multi-meter. Nothing hot just my mind :). – Builder Jun 29 '16 at 13:26
  • @Dave X, on 7.2v battery, 3.7v. On 11.1 battery it is 5v. – Builder Jun 29 '16 at 13:27
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You really could benefit from a DC/DC switching power supply. For instance you are wasting about 20% of the power of the 7.2V battery and something like 50% of the power of the 11.1V battery.

That said, could it be that you are triggering the 3 ultrasonic HC-SR04 too closely together? If you don't wait for the sound to die out from the 1st sensor the 2nd sensor could give unexpected results. Same goes for the 3rd sensor.

  • Is this an answer to the question Now my question is if the power is below 5v, does sensors starts behaving like this? How can we supply voltage so every sensor will receive full 5v to work properly? – MatsK Aug 2 '17 at 7:15
  • No. But it appears that the author was having difficulties phrasing the question. And that the actual goal was a working "autonomous track vehicle". In the end I believe this question suffers from the XY Problem. – st2000 Aug 2 '17 at 12:25
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Your 7805 regulator isn't working, it should have a output of 5v, 3.72v is way off. 2-4% diff from 5V is the normal specification. https://www.fairchildsemi.com/datasheets/LM/LM7805.pdf

Vin should be between 7-20volt even if the datasheet indicate that you can have as low as 5volt in.

Causes could be:

  • Wrong design
  • Low battery voltage
  • Faulty component
  • Faulty connection

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