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Topic: Arduino breadboard ADC question!! (Read 1 time) previous topic - next topic

nick321

I  let my ADC reference voltage=5V

but my analog signal can't reach the 5 volts, it'll cut off the signal about 4.5 volts

but I used the arduino uno the signal  can reach the 5 volts

so  I'm very confused what's wrong with my breadboard arduino????

septillion

What do you mean, can't reach the 5V? You have to supply the 5V.. Or do you mean you already have a reading of 1023 @ 4,5V? If so, with what do you supply the micro controller? Probably the voltage of that is just 4,5V
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jack wp

Did you use a VOM to test that voltage? Or some kind of script?
The 5v regulators may vary a bit from each other..
Put some caps on the 5v rail, and put a 0.1uf cap on the analog pin.
What are you trying to measure?

nick321

YES, I already used the VOM to measure the VDD and GND it's 5 volts

I am measure the sensor signal and I just amplify the siganl and  through the low pass filter, I'm thinking is there any possible about impedance matching..........I'm not sure

septillion

Please answer all the questions...
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DVDdoug

Is it a problem if it won't go to 5V?    Is it supposed to go to 5V?

Quote
I am measure the sensor signal and I just amplify the siganl and  through the low pass filter, I'm thinking is there any possible about impedance matching..........I'm not sure
We need to see your schematic.

We don't know anything about your signal, your amplifier, or your low-pass filter.

If your amplifier and/or low-pass filter uses an op-amp, and the op-amp is powered from 5V, you can't usually get the full supply voltage from an op-amp.   Similarly, the output of an op-amp generally won't go the negative supply, or it won't go all the way down to ground if there's no negative supply.

jack wp

What does your VOM read on the analog pin?

raschemmel

This is nonsense.
Please state what you are measuring .
Your analog signal does NOT need to "reach" 5V . 5V is simply the FULL SCALE voltage. The ADC can measure anything from 5 mV to 5V. Obviously you have a misunderstanding about ADCs and how to use them. Start by explaining


Quote
I am measure the sensor signal and I just amplify the siganl and  through the low pass filter, I'm thinking is there any possible about impedance matching..........I'm not sure 
First of all, the only way to AMPLIFY a sensor signal is add an AMPLIFIER. The fact that you are not aware of that means you need to start at ground zero. An LPF (Low Pass Filter ) does NOT amplify. It Filters (out)  (duh) high frequencies. If it was a high pass filter it would filter (out)  low frequecies.

1- what is the sensor ?
2- do you have a clue how to make an amplifier ?
3-how much electronics experience do you have ?
Do you have a DMM (Digital Multi-Meter) (NOT VOM) ?
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nick321

1. it's a Piezoelectric film  sensor
2. I just used the charge amplifier+Sallen key lowpass filter=band pass
I add the DC offset 2.5V

and I already used oscilloscope to measure my analog signal

and my signal just look like a sine wave

I think I need to measure the AC signal from analog inputs

raschemmel

#9
Oct 07, 2015, 10:02 am Last Edit: Oct 07, 2015, 10:21 am by raschemmel
We need to see the schematic of the circuit.
What charge amplifier ? What's your gain ?

Do you know the difference between ac and dc ?
If so, then what's your problem ?
If you know anything about electronics then you know you havd to tell us the frequency, amplitude, and voltage range of the ADC input signal.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

liuzengqiang

If you believe your signal is 5V but arduino only says 4.5V, can you use a multimeter or scope together with arduino and see if you still have the discrepancy.
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raschemmel

Quote
If you believe your signal is 5V but arduino only says 4.5V, 
More importantly, why do you care that the voltage is only 4.5 V if it is a sensor value ? You didn't post a schematic and you didn't answer the question about how you amplified it or the gain.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

liuzengqiang

More importantly, why do you care that the voltage is only 4.5 V if it is a sensor value ? You didn't post a schematic and you didn't answer the question about how you amplified it or the gain.
Because OP thinks he should get 5V. If that's the issue, use both measurements and confirm it.
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raschemmel

Quote
Because OP thinks he should get 5V. If that's the issue, use both measurements and confirm it.
I'm not suggesting he shouldn't get 5V but he hasn't explained why he thinks he should get 5V from an analog sensor. He never said it was a digital sensor and the fact that he's trying to read it with an analog input means he thinks it's analog. Have you ever run across and ANALOG sensor that outputs 5V ? Doesn't that strike you as odd ?
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

liuzengqiang

Nothing is clear about what OP is doing so let's just hope he comes back.
Serial LCD keypad panel,phi_prompt user interface library,SDI-12 USB Adapter

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