Short distance radio communication (30-40 cm)

Question

Do it yourself

Essence: There is some “base” and two devices (for simplicity we will call them light bulbs) located at some distance from it. While the bulbs are in the range of the base, nothing happens, but as soon as they go beyond this zone (30-40 cm), they start flashing. There will be no information transfer - you just need to determine whether the bulbs are near the base or not, that is, bandwidth, noise immunity, and the like are not critical at all.

Requirements: Autonomous power supply, minimum power consumption, minimum dimensions and weight.

Question: How to organize such a connection? The distance to the base is quite critical - it should not be too small or too large (I indicated the approximate distance a little higher).

Answer 1

If you need the system to work at a strictly defined distance, then this will be very difficult. It’s a bad idea to tune in to the signal level - it can float a lot (reception conditions change, it’s difficult to make a receiver and transmitter with very accurate and stable parameters in terms of power / sensitivity, etc.).
Making a full-fledged radio frequency range finder is very difficult, even if not very high accuracy is needed.
In general, the implementation of this rather simple idea on a radio transmitter / receiver will be very difficult.

Answer 2

In such a situation, probably the simplest and cheapest option would be an uncle with a ruler. Of the electronic options - perhaps a pair of ultrasonic or sound transceivers (speaker-microphone) with distance measurement by delay or phase shift. For radio, the distance is too short - very high frequencies are needed, it will be difficult to implement and debug.

Answer 3

make a circuit on the bulbs and an open container on the base. Power the key from the circuit through the diode, which turns off the blinking.

Answer 4

The first thought is that the base is active and the clients (bulbs) are passive. What if it's the other way around? Let the light bulbs “beacon” every 2-3 seconds (for example, with an acoustic click or in any way convenient for you, 1-5 GHz radio, it doesn’t matter), and the base equipped with 3-4 sensors triangulates by delays. Advantages - you can calculate not only the distance, but in general the coordinates of clients. Do you understand what I'm talking about?

Answer 5

If everything is as described in the question, you can use a simple inductive connection, as in wireless mice with a base. In reality, the signal will be felt just from 30-40 cm.
But again, depending on what kind of devices, there are solutions based on optics (infrared is simpler and cheaper, ultrasound is more complicated and more cumbersome, a classic radio channel with reduced receiver sensitivity).

Answer 6

I would read Wikipedia, for a start (http://ru.wikipedia.org/wiki/Proximity_sensor) and decide on the principle of operation.
And then I would probably look in the direction of magnetic contact sensors or magnetoresistors. Optical sensors, for example, such: qps.ru/0VfM4 , here you already need to choose the principle of operation, depending on the working conditions and look, according to the manufacturers' catalogs, what is for your task.

Answer 7

"even if not very high accuracy is needed" - this is certainly powerful