Cheapest object sensor on the market!

The design constraints would be satisfied by a bit of wire that's pushed onto a solder pad, so perhaps there are unstated considerations?

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even integrate it on or print it on my circuit board, My project is to no to pass a total cost of $1 (Sensor, cheap Liquid Cristal display, coi Battery with a hight not more than 3mm. I need a product that last only 3 hours of use. Low life sensor, whichever would be the cheapest solutio (touch, reflective, capacitive or photosensor).

Where should i found one or may be how to do one on the circuit board.

If you are looking for a low-life sensor, you will find that many humans have one integrated. Perhaps you could find a dealer in surplus humans and salvage them for parts?

You need to clarify just what the hell you mean by an "object sensor" if you expect any useful help.

If you mean buttons, then the cheapest solution is rubber w/ conductive base. Rubber buttons are approx. 25 cents. The contact points are on the PCB, using uC debouncings. You also mention LCD, which would be difficult to do without uC or a dedicated controller.

How about the crude touch-sensors from early tv remote controls (think

These where just two electrodes (part of the PCB) and a very simple analog transistor-circuit that measures the presence of body-resistance.

Won't work for users with gloves on, but it will be cheap for sure.

Nils

What are you trying to measure ?

Any thing moves or waves in front of it, in my case to detect hands.

If you mean buttons?

No, i will use a smart card type size, thickness can go as hight as 3m max.

Any idea on a solution?

What are you trying to measure?

I am not trying to measure a distance, but want to detect a hand or finger when it comes within 50mm to 100mm.

Can you detect change in lighting?

Thanks Nils, as I will try your advice once i ran our of the other option as touch would be my last one.

Do you have another option (not touch) as cheap as the one above tha detects within 50mm to 100mm?

I only need to detect the presence of a hand! if detect change in lightin maybe in a situation where a changing in room lighting might get i conflict without the presence of the hand, how would i control it in orde not to happen?

You can detect rapid change in lighting, or even temperature if the finger is close enough.

You are not telling us what to do with the hand wavings. If you are using it to turn on the device, false triggers (room lighting changes) might not matter. If you are using it to count votes, then it does matter.

Devices like motion-sensitive toys use an AC-coupled circuit triggered by a change in the resistance of a CdS cell. It's very cheap, but will be triggered every time the lights in a room are switched off and on.

Google "digital theremin". With essentially a schmitt-trigger inverter and a few passives, you can create a capacitance-based circuit to detect the approach of a body part. But it is fairly difficult to design one that is tolerant of voltage and temperature changes. Easier with a micro. TI also has an app note on doing this with an MSP430F20xx, which is very cheap in large quantity - well under your price target.

Ok, great! which would be the cheapest solution?

Probably not. The OP wants $1 total BOM. Lets figure 0.25 for PCB,

Every time the device detects object in this case hands or fingers, i nee it to count votes as long as its on. any advice?