My first post. I did search, but did not find an answer so sorry if question is duplicated.
I would like create a battery powered device with 30 LEDs that are triggered by a defined range of EMF strength. Each LED would be independently triggerable and would be lit for a minimum of 3 second or the length of time the condition is met.
Which Arduino would be best suited for this type of task? How many would be needed to control 30 LEDs?
Parts list:
Arduino(s)
LEDs
Resistors
EMF sensors
Wire
Anything else?
If only one led is lit, it could be done with 6 Arduino pins and 6 resistors, using a technique called charlieplexing.
If up to 30 LEDs must be lit, it is more difficult, but there are various circuits that can be used.
Charlieplexing can still be used, but some extra transistors will be needed. The code also becomes more complex because the Arduino will need to multiplex the LEDs.
Alternatively, additional chips can be used such as 74hc595, pcf8574, max7219 or pcf8575.
Another alternative would be a strip of 30 WS2812 LEDs.
With any of these ideas, any Arduino should be fine, and only one would be needed.
EMF is AC and is usually detected by sharp pointed probe. That AC is rectified and applied to a resistor voltage divider. The DC is then read by your Arduino A/D port. Is this what you had in mind?
Thank you for all the responses! Only one LED should light at a time. If multiple LEDs light at once it would be considered an error. They are not graduated, but each would detect for an area approximately 2x2". In looking at more options, I think a magnetometer may be better suited to my needs. The strength detected would be low, say 500Hz-1kHz. I won't waste more of your time until I know better what I'm doing. And at the risk of being laughed off the board, I'm wanting to make an electronic Ouija Board that will light an LED for a given letter of the alphabet in response to a change in EMF around a sensor. 1 sensor per letter plus Yes/No/Hello/Goodby. Thanks again!
Not necessarily so. Imagine a row of 5 sensors and you place your finger over one and an LED lights up. In scenario 1 you remove your finger immediately, but I want the LED to light for 1 second before shutting off as a confirmation so I don't miss it. In scenario 2 you hold your finger over the sensor and the LED remails lit until you move it. That's okay too as long as you don't use 2 fingers. At least that was my logic...
I appreciate your explanation of charlieplexing. That should help for sure. As for the device creating the EMF, that would be a ghost of course. As for controlling the range, I am hoping that experimenting with the sensor sensitivity will help dial in the desired affect.
How do you find a ghost with adjustable EMF? Since you are using a human body as an antenna, it will pick up all kinds of stray EMF, not necessarily the emf you want. Consider florescent lights. Consider the electrical wiring in the room.
Great questions, and I have no idea. It's just a silly project with no real use or future purpose. But since you mentioned it, would a person, just sitting by the sensors, act as an antenna or only if you are touching it? Thanks!
Any antenna receiving RF also radiates the the same RF. That is the basis of all Yagi type antennas. The contact is very low resistance, so is just like touching two wires together.
As for controlling the range, I am hoping that experimenting with the sensor sensitivity will help dial in the desired affect.