Arduino clone, and unwanted noise

Question

I am somewhat new to DIY electronics, and I am having a go at Arduino.

Having succesfully made a simple door alarm using a PIR sensor and some parts of my old car, I am now trying to create the classical clap-on clap-off contraption. However I am having trouble tuning the microphone. The setup is fairly simple, having the electret microphone routing it's analog output to the Arduino's analog input - which is reading the voltage. The arduino maps input voltages between 0 and 5 volts into integer values between 0 and 1023.

The problem is that the input signal when literary NO sound (even when I disconnect the microphone all by itself) is always reading values between 850 and 860. Having the microphone connected may differ these values from 1 to 3 integers, where 1 is simply when the microphone is ON, and 3 is me tapping the membrane with my finger(!).

Needless to say, this is not particulary good. I have tried with another Arduino clone, and another electret microphone - with no luck.

QUESTION: Is the general quality of cheap electronics parts of for example eBay, really that bad compared to the genuine more expensive parts? Eg.: My Arduino clones each went for 3 dollars, compared to the genuine product approximately 20 dollars.

PS: I am also relatively new to this forum, so I am hoping this is an okay question to ask.

• Ignacio Vazquez-Abrams: The answer is no.
• Scott Seidman: How are you connecting the microphone? Do you have any sort of preamp circuit?
• pjc50: Show us a circuit. You almost certainly need a preamp and bias.

Answer 1

I used Arduino clones few times without issues, it's open standard with no extra fancy parts, so unless it's really poor one and/or you're very unlucky all tends to be fine.

As for floating ADC reads this is rather typical behaviour, this is effect of noise on power supply voltage. This applies especially when microcontroller is powered from USB port of your computer or wall plugged power supply, but even on batteries track on your PCB can pick up noise (for example from nearby electrical devices. If your application needs more precision (for example alarm triggered by noise detector) you can take a few measurements, calculate mean value and use it instead.

I don't really understand "1 to 3 integers" part of your problem. If you mean that plugged microphone gives one digit reads (1-9) and when it is knocked with finger signal is two orders of magnitude stronger (3 digit number, 100-999), then this is actually what I would expect.

• E. l4d3: Thanks, that was really what I wanted to know. About the unclear part, what I meant with 1 to 3 integers was increment within the 0-5 V space (0-1023). When microphone plugged, I can change the value from eg. 850 to 853.