How to prevent a bluetooth module noise disturbing sensors connected to Arduino adc-inputs?
My hobby system for electric bicycle data gathering (and control) currently consists of an Arduino Mega2560, a breadboard with several sensors, powered by 6 pcs of AA-batteries or an usb connecion to a laptop (during programming).
There is also a bluetooth circuit containing Wireless Bluetooth RS232 TTL Transceiver Module - air.
The bluetooth module sends sensor values all the time to a Nokia E72-1 mobile phone to display and to a file during riding.
When the wireless circuit is removed from the breadboard, the sensors vary their output to the adc only by half or one step (out of 1024), when constant data is expected. That is ideal, very good. Even when the test duration is minutes and tens of thousands of adc conversions, the adc values are ideal.
With the bluetooth circuit on the breadboard the sensor output vary giving typically 5-7 different values (out of 1024) instead of 1 or two . All the sensors vary in the same way so the reason is assumably noise generated in the power and ground lines. Accurate adc -values are necessary due to limited range of “interesting” values e.g. from a pitot tube. The the existence of the bt-module is enough to cause significant noise, connecting and sending causes a little more noise.
(When power is taken from the usb instead of batteries, the adc output varies also with typically 4-6 values; during riding there is no usb so this is no problem)
I have 0.1 microfarad capacitors near the circuits, a 10 microfarad capacitor on the rails of the breadboard, and 10 ohm resistors as “Grumpy_Mike” describes on the page
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
. No inductors tried yet, however. The wire layout resembles “a star configuration”, with the connection point being the ground rail of the breadboard.
How to prevent the noise generated by the bluetooth module to disturb sensors? Options:
- adding inductors, capacitors, resistors to isolate bt module better? How?
- using a separate regulator chip to on the breadboard give power to the bt-module? ( bt needs about 35 milliampers of 5 V).
- using another Arduino board (e.g. Arduino Nano) to take care of the bt communication. Arduino mega communicates with the Nano through I2W or SPI (or…?) ? Both Arduinos must be connected to the same power source of 6 AA batteries (7- 8 Volts).
- something else, what?
In the alternative 3 I am afraid that when the power rushes to the circuits or is disconnected there might be short moments when some of the circuits are powered and some are not, leading to the destruction of microchips or circuits. (I may be too worried about these things after burning one Arduino Nano, http://forum.arduino.cc/index.php?topic=174799.0 )
I am searching a relatively simple solution (non commercial, one time project for myself).
Any links and advice are appreciated.