If you look at the Elsa singing doll toy, it trigger the music/singing when you touch both hands. Also, this toy can stay inactive for months on only 3 little battery I am assuming they are "grounding" the circuit through our body.? can it be?
\$\begingroup\$
\$\endgroup\$
Add a comment
|
2 Answers
\$\begingroup\$
\$\endgroup\$
3
It will probably be an a.c. voltage applied to the metal contacts so that it can capacitively couple through the skin, rather than having to have a high impedance d.c. input that will be subject to spurious triggering problems. As such, it could employ sporadic pulses, since the triggering does not have to happen extremely rapidly after the contacts are closed. For example, a 1µs pulse could be generated every 100ms, for a duty cycle of 0.001%. This will allow the average power dissipation to be reduced by the same factor.
-
\$\begingroup\$ to get a pulse every X ms. you need a microcontroller? wouldn't it suck up the battery? \$\endgroup\$ Commented Mar 26, 2016 at 22:29
-
\$\begingroup\$ @Jean-PhilippeAuclair ti.com/product/TPL5010 \$\endgroup\$ Commented Mar 27, 2016 at 1:29
-
\$\begingroup\$ Truly awesome chip! \$\endgroup\$ Commented Mar 27, 2016 at 1:53
\$\begingroup\$
\$\endgroup\$
1
Indeed it can be. Notice that Queen Elsa has a metal contact in the palm of each hand. A very low voltage is applied to the contacts, and if any current flows the speech output is triggered.
The circuitry involved is, as you realize, very low power, but (just as an example}, if the batteries have 100 mA-hour capacity, and the detection circuitry takes 50 uA, the batteries will last for about 2,000 hours, which is about 80 days or 3 months.
The total circuitry (including a microcontroller) does not have to be powered on most of the time. All that is needed is the detection circuit being able to turn on the rest of the circuit when a touch is detected.
answered Mar 26, 2016 at 17:29
-
\$\begingroup\$ But what would be this "detection circuit"? \$\endgroup\$ Commented Mar 26, 2016 at 22:28