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I’m a Jack of all trades sort of guy but have basically zero electrical knowledge..

That being said.. I want to use a live.. real plant...to turn on and off a light. I tried a touch switch replacement but it didn’t meet expectations... touching the soil or the stems would trigger the switch but the actual leaves didn’t work..

Would anyone know of a way to strengthen the signal so it reaches down the leaves? Or of another way to make it happen? Perhaps messing with a proximity sensor?

I have such a lamp...one that I fixed recently, it’s 40 years old and works great.. I replaced the ground lead and the copper foil that it ran to... underneath the soil .. I looked at the electronics and they were pretty old-school… I was hoping not to have to re-create that but rather use something new and groovy.. my 1 year old granddaughter plays with it all the time so I want to make her one for Christmas.. Ideas? Thanks Eric

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  • \$\begingroup\$ Try celery! (Very wet.) Don't use rubber plants (Ficus elasticus.) Also, see this article ;). \$\endgroup\$
    – jonk
    Dec 9 '20 at 0:31
  • \$\begingroup\$ I get lots and lots and lots of links on a web search for "plant touch switch" - I'd suggest reading some of them and see what clues you can pick up \$\endgroup\$ Dec 9 '20 at 3:56
  • \$\begingroup\$ I know of one company that sells a light you basically cover with dirt ‘plant a lamp’ I bought one years ago for a sister-in-law but it never worked well. It had an adjustment screw as I recall and was too fussy. \$\endgroup\$ Dec 9 '20 at 4:11
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It's very unlikely to work. Those switches work because touching them creates a capacitive path to ground, through your body, which then alters the frequency of a resonant circuit or something like that. The plant is a pretty poor conductor, so touching the leaves has very little effect on a sensor all the way at the base. Sure, there are ways you could possibly crank up the sensitivity of the sensor, but assuming they worked, you would end up with a device that also turned on the light any time a breeze moved the leaves or someone walked within 6 feet of the pot.

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    \$\begingroup\$ No it works and pretty well too.. I got this for my wife at the local florist around 1981.. youtu.be/PmgAY6PWWTc ( Video of my old one) I was just hoping I could adapt a replacement touch sensor as they are readily available I tried a "Zing Ear TP-01 ZH Touch Lamp Light Dimmer Switch Control Sensor" dirt and stems did switch light but leaves don't. \$\endgroup\$ Dec 9 '20 at 2:44
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OK, we're engineers not biologists but entertaining a child is a worthwhile endeavor, so here's what I'd try:

  1. Wrap the stem of the plant with foil (copper tape or aluminum foil), putting the touch plate wire inside that wrap. This will couple capacitively to the vascular channels that run through the plant. Don't stick the wire in the dirt, that just adds a large undesired capacitive load.

  2. Give the plant a generous feeding of liquid fertilizer, one that has plenty of minerals. Don't use too much plain water either. As this new mix rises in the plant's vascular channels -- which may take a couple of days -- it should increase the conductivity of those channels, making the rest of the plant more sensitive to touch.

  3. The touch circuit may be self-calibrating, so unplug the light and re-plug it after you've done the above.

  4. Finally, when the child is about to touch the plant, hold their other hand yourself, increasing their capacitance to ground. Here's hoping it works!

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  • \$\begingroup\$ Thanks Mark, I'm telling you, I own one and it requires no special care.. I have replaced with different plant varieties. youtu.be/PmgAY6PWWTc \$\endgroup\$ Dec 9 '20 at 21:01

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