Cheapest object sensor on the market!

On Apr 6, 1:15 pm, "raedarrar" <i...@0-800.tv> wrote:
> What are you trying to measure?
>
> I am not trying to measure a distance, but want to detect a hand or a
> finger when it comes within 50mm to 100mm.

Can you detect change in lighting?

>How about the crude touch-sensors from early tv remote controls (think 
>70th)?
>
>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
>

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

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

>On Apr 6, 1:15 pm, "raedarrar" <i...@0-800.tv> wrote:
>> What are you trying to measure?
>>
>> I am not trying to measure a distance, but want to detect a hand or a
>> finger when it comes within 50mm to 100mm.
>
>Can you detect change in lighting?
>

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

On Apr 6, 1:54 pm, "raedarrar" <i...@0-800.tv> wrote:
> >On Apr 6, 1:15 pm, "raedarrar" <i...@0-800.tv> wrote:
> >> What are you trying to measure?
>
> >> I am not trying to measure a distance, but want to detect a hand or a
> >> finger when it comes within 50mm to 100mm.
>
> >Can you detect change in lighting?
>
> I only need to detect the presence of a hand! if detect change in lighting
> maybe in a situation where a changing in room lighting might get in
> conflict without the presence of the hand, how would i control it in order
> not to happen?

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

On Apr 6, 1:54 pm, "raedarrar" <i...@0-800.tv> wrote:
> >On Apr 6, 1:15 pm, "raedarrar" <i...@0-800.tv> wrote:
> >> What are you trying to measure?
>
> >> I am not trying to measure a distance, but want to detect a hand or a
> >> finger when it comes within 50mm to 100mm.
>
> >Can you detect change in lighting?
>
> I only need to detect the presence of a hand! if detect change in lighting
> maybe in a situation where a changing in room lighting might get in
> conflict without the presence of the hand, how would i control it in order
> not to happen?

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.

On Apr 6, 5:02=A0pm, linnix <m...@linnix.info-for.us> wrote:

> You can detect rapid change in lighting, or even temperature if the

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.

On Apr 6, 4:22=A0pm, "raedarrar" <i...@0-800.tv> wrote:

> Do you have another option (not touch) as cheap as the one above that
> detects within 50mm to 100mm? =A0

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.

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

Ok, great! which would be the cheapest solution?

> MSP430F20xx, which is very cheap in large quantity - well under your
> price target.

Probably not.  The OP wants $1 total BOM.  Lets figure 0.25 for PCB,
0.25 for LCD, 0.40 for LCD controller.  The uC needs to be less than
10 cents.

>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.
>

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