Noise with 6 PING (ultrasonic) sensors - which capacitor to use?

Other Hardware General Electronics
1

Hello,
I wonder whether I could get some help with capacitor choice?

If I use 6 PING sensors (each 25mA) with Arduino Uno (USB powered) the signals are jumping around.
If I use 1 PING that the signal is steady.

Could anyone advise me how to and which capacitors to use to smooth the signals?
Should I use a capacitor parallel with the main power wires (5v and ground)?
Would it help if I powered the Arduino board with external AC/DC (more amp than USB)?

Thank you, all the best, K

2

(I'm assuming that each Ping has its own I/O pin.)
The/A "Ping" is a current hog.
If you are trying to run 6 from the arduino "5V", that verges on too much.
Find out. You say one is OK. How about two? Three?
When does the scale tip?
You should implement a separate +5V to run all those (6) Pings.

3

Do they really take 25mA continuously, or spike to that when operating?

4

Please give a link to what ping sensor you are using.
This has an effect on how you decouple the power supply.
I would guess you need at least 100uF on each ping unit. You might also need some low value series resistors or inductors as well, like shown here:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

5

these are the pings:

The more pings I have in the circuit the more spikes, but I will check after how many being used it gets annoying.

I will get some 100uF decoupling capacitors and give them a try.
thanks, K

6

Yes put them on each unit across the +5V and ground as close to the unit as you can get.
If you can, get a small choke (inductor) to link the 5V on the sensor (and +ve end of the capacitor) to the 5V supply.

7

Do they really take 25mA continuously, or spike to that when operating?

Parallax's store page mentions a 25mA figure, but the device's PDF states 30, 35mA.

8

if I use 5 PINGs without any caps nor choke that the signals are fine.
I think it is very important to experiment with the placement of the PINGS (they shouldn't face the same direction) and with the delay times.

however, I will add a servo to the circuit, so I am sure I will need the caps, ... to be continued. thanks, K