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Topic: Circuit Help (Read 669 times) previous topic - next topic

wwdd

Aug 21, 2013, 04:33 pm Last Edit: Aug 21, 2013, 04:37 pm by wwdd Reason: 1
Hello everyone. So, my project worked fine on the breadboard. But once soldered on the arduino it has decided not to work.
1. The pressure transducer outputs a frequency reading. If i connect a dmm to DI5 and the arduino ground, there is no reading. If i connect the dmm to DI5 and the battery ground I get a reading. If i connect the circuit to the serial port I get no readings, and I assume this has something to do with the grounding. If I ground the arduino gnd pin to the battery gnd, DI5 has a reading of zero. Any clues as to what I am doing wrong? (circuit diagram attached)

2. Do i have to add anything in between the battery and the arduino if I want to use the same battery to power the circuit as well as the arduino?

groundfungus

The pressure transducer ground needs to be connected to Arduino ground.  The huge picture is a pain.

wwdd

Quote
The pressure transducer ground needs to be connected to Arduino ground.  The huge picture is a pain.


There should be a smaller picture there now. When I connect the transducer to the arduino ground instead of the voltage regulator ground/battery, No voltage goes to the transducer.

Henry_Best


Quote
The pressure transducer ground needs to be connected to Arduino ground.  The huge picture is a pain.


There should be a smaller picture there now. When I connect the transducer to the arduino ground instead of the voltage regulator ground/battery, No voltage goes to the transducer.
Connect all the grounds together.

MarkT

All grounds should be commoned.
[ I won't respond to messages, use the forum please ]

MarkT

Or put another way a circuit is a _circuit_, so there must be two wires minimum linking any part of the circuit
to the rest of it.  If not you have an aerial, not a circuit.
[ I won't respond to messages, use the forum please ]

wwdd

When I connect all the grounds in the circuit, I no longer get any readings from the transducer. I've checked and rechecked my soldering to make sure that everything was wired correctly.

jackrae

Details of opamp, PT and regulator please.
Why the resistor before the regulator
Values of C and all resistors please
We cannot analyse a circuit unless values and component numbers are given.

wwdd

OPAMP: LM124J The purpose of which is to level shift the response from the Pressure transducer above zero.  http://pdf1.alldatasheet.com/datasheet-pdf/view/27206/TI/LM124J.html

Pressure Transducer: Outputs a frequency response for a change in pressure. Frequency is in the 36-38kHz range.

Voltage Regulator has a resistor in front of the positive terminal because the voltage regulator was getting too hot. This seemed to correct the issue.

Resistor values in the op amp circuit are all the same R=1000 ohms

Resistor prior to voltage regulator R=75 ohms

Capacitor = 100nF

jackrae

Xc for the 100nF capacitor at 36kHz works out at 44ohms which is quite a load on the OP ampl. 
Assuming the OP amp outputs a nominal 1.5 volts the arduino input signal will be around 63mV

Assuming a 0-5volt input sensitivity equating to 1023 counts then you are looking at somewhere around 12 counts.

Why not omit both the capacitor and OP amp output resistor and see if that helps - after joining all the grounds.

Have you confirmed the transducer is getting a suitable drive voltage and is outputting a signal.

wwdd

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Why not omit both the capacitor and OP amp output resistor and see if that helps - after joining all the grounds.


I just tried this, but to no avail. Still reading zero at the serial port, as well as at pin 5. Although, if I touch the multimeter to the output pin of the opamp I get the right reading, but it is not translating over to pin5, even though they are directly connected, which I confirmed by a continuity test. Could it be possible that i have somehow damaged digital pin 5?

Quote
Have you confirmed the transducer is getting a suitable drive voltage and is outputting a signal.

Yes, I have confirmed that the transducer is getting suitable voltage.

wwdd

I was mistaken before. There is no reading from the op-amp output. There was a problem with continuity. I have replaced the op-amp with 2 others testing to make sure it was not the op-amp, although it made no difference.

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