sensors requires 10-30 vdc, want to use external power supply but not sure

Hi, I have been building since last summer an arduino weight scale using 4 pressure sensors and some hydraulic jacks.

Everything should work ok (I asked here before about a lowpass filter to deal with noise signal, tried purging air out of the hydraulic cylinders, …), but the analogread results are still very erratic. I suspect the power requirements of the transmitters are not being met: the sensors need 10-30 vdc to work with 4-20 amp outputs but I am using a 9 volts battery for the sensors and another 9v battery to power the arduino.

I would like to use an external power supply that I have from a small ta2020 audio amplifier, it says: output: dc 14.0v - 4A.

I am not sure how to proceed, other than the obvious, to try to connect the power supply to my project using the right adapter that fits the supply and then wire the +, - accordingly to my board and sensors. However I know this is wrong because the arduino works with 3.3V or 5V and this could fry my project, would a diode be enough to protect my board? and do I run the risk of burning my sensors somehow using this power supply instead of the 9 volts battery I have been using?

Thanks!

Thanks

the sensors need 10-30 vdc to work with 4-20 amp outputs

That’s milliamps, right? 4-20mA is an industrial standard, but I’m not up-to-speed on details. You’ll need to convert that current to a voltage. I’d guess you can do that with resistors, but you might need an op-amp circuit of some kind. I suggest you do some research on that if you don’t get an answer here.

[u]Here[/u] are some over-voltage protection circuits.

The TA2020 is an audio power amplifier designed to drive speakers (4 or 8 Ohms)… It’s not right for this application. The Arduino’s analog inputs are very high impedance (100 mehohms) so they require (almost) no current or “power”. If your signal is below 5V you may need some voltage amplification but you don’t need a power amplifier. (And, it’s possible that you need some signal amplification even if your sensors are running on 9V.

but the analogread results are still very erratic.

Your sensors are probably built-around strain gauges. These things put-out a tiny voltage which makes it difficult to get a good signal-to-noise ratio. Some [u]smoothing[/u] may help, or you may need something “different” on the analog side. An amplifier amplifies any existing signal and noise together and the active electronics will actually add some noise, so it can’t improve the signal-to-noise ratio.

the sensors need 10-30 vdc to work with 4-20 amp outputs

If you mean 4-20 mA outputs, just use a 250 Ohm resistor in the ground lead, and read the voltage using analogRead().

See below.

To protect the analog input from overvoltage, add a 10K resistor in series with the sensor output. To optionally reduce noise, add the 100 nF capacitor, C1. Don't forget to connect all the grounds.

sensor.png

sensor.png

But is it unlikely then the problem is that 9 volts provided by the battery I am using are not enough for the sensor to work properly?

I am not excited about using a power supply with my project because I will be using it on my ranch "off the grid", so maybe I should skip this idea and try other things. But the manual reads: An external power supply delivering 10-30 VDC with minimum current capability of 40 mA DC (per transmitter) is required to power the control loop, I wanted to try it to see if finally I can get usable results.

I tried for several days to smooth the signal with some ingenious sampling, but the sensor is failing to provide consistent results on very simple experiments like weighing the same object two times in a row. If the battery does not suppose a problem then I will try to bleed the air out of the hydrualic jacks again, or redo my circuit to see if something comes up

Thanks!

If the manufacturer tells you to use 10 to 30 V to power the sensor, it is not a good idea to use 9 V.

Also, 9 V block batteries are for smoke detectors and won't power an Arduino for more than a few minutes.

Using sensors and Arduinos "off the grid" requires an entirely different approach than disposable batteries, unless you are willing to travel out to change them every few days.

You will probably need a solar panel, a charge controller and a rechargeable battery (lead acid is great) for your system.

Why do you refer to 'will try to bleed the air out of the hydrualic jacks again'. What has this got to do with the sensors?

Please post a model or diagram of the unit.

There are other batteries other than the 9v, why not go 12v then you can get a rechargable lead acid or use 2 x 6v lantern batteries in series. You can run the sensors direct off the battery and your Arduino through the regulator on the Arduino.

Daz

Hi!

If there air bubbles inside the cylinder the pressure will not be constant with a given weight or will be very suceptible to small movements, which is my problem somewhat. (I filled completly the cylinder jacks with hydraulic oil with a syringe while purging the cylinder with some pliers until I could see no more air bubbles. Then I screwed in / connected the sensor to the cylinder. )

I will try with another battery then, I was reading about using an acid battery like you suggest, I am going to search for some posts on advices on how to use a car battery or acid battery, tomorrow I will post a diagram, I will try to do a more basic prototype with only 1 sensor and an arduino with JACK port (Im using a LoRa 3.3 arduino) without soldering with a breadboard and with different batteries and then I will post a schematic, I am still learning how to draw schematics,

thanks!

switchmode power supply

Daz1712:
Why do you refer to ‘will try to bleed the air out of the hydrualic jacks again’. What has this got to do with the sensors?

Please post a model or diagram of the unit.

There are other batteries other than the 9v, why not go 12v then you can get a rechargable lead acid or use 2 x 6v lantern batteries in series.
You can run the sensors direct off the battery and your Arduino through the regulator on the Arduino.

Daz

Thank you for your reply.

I learn something new every day.

Daz

JoeJosefo:
Im using a LoRa 3.3 arduino

Could you please post a link to the exact type of Arduino you are using?