Light Up a Toy Greenhouse

We had a plastic toy greenhouse lying around unused for 2 years, dirty and with a few pieces missing. Time to fix and upgrade it for a second life!

The upgrade is easy, but the effect is dramatic: it’s been given artificial lighting. It looks cool and plants will grow faster when they are kept indoors in the dark and cold season. But most important of all, it now has an electrical switch, so kids love it! And that makes it a great tool to teach about photosynthesis and about modern food production techniques.

The whole project was done in an evening with in-stock or discarded components.

Here's what I used:

• A plastic toy greenhouse
• 50 cm of adhesive LED strip (30LEDs) rated for 5V
• A USB power supply rated for 0.55A
• A USB cable
• A toggle switch
• 50 cm of stranded hookup wire

Let’s throw away the old earth, give it a good wash, and fill the pots up with new potting earth. Put in some basil seeds and water it. All the work will be done on the roof and the seedlings won’t need any light in the first week anyway.

Collect the materials. I had white LED strip left over from another project. It is made for 5V, and every LED has a 120Ohm resistor in series. So the expected current is I=(Vcc-VLED)/R=(5.0-3.0)/120=0.017A. Multiplied by 30, that gives a total of 0.5A. When I applied 5V, it drew 0.4A, close enough. If you buy LED strips on purpose for this, I suppose it’d be better to buy grow light strips that emit a spectrum optimized for plant growth.

This means for the power supply we can use a USB supply from the pre-smartphone time, I still had 3 lying around with a current rating of 0.55A, perfect!

Next is a cable: also from the pre-micro-USB days, I had 3 cables with weird proprietary connectors on the receiving end of the power. I cut it off and picked out the red (for +5V) and black (for 0V) wires to be used on the LED strip. Check that the output is 5V and that the LED strip lights up well when connected!

Pick a toggle switch. I choose a 6-pin double-throw double-pole switch. A simple 2-pin single-throw, single-pole would do as well, but this one looked better, and the extra pins actually make it easier to attach the USB cable to the LED strips.

Finally, get 50cm of multi-strand hookup wire. I recuperate this from discarded electronic devices. It’s always good to stick with color conventions, so 25cm red wire and 25cm black wire.

Cut the LED strips in 3 equal pieces of 10 LEDs each. There are copper contacts between every LED, so they can be cut and connected anywhere. Cut the stranded wire in 2 pieces of 5cm (for the central strip) and 4 pieces of 10cm (for the lateral strips). Strip the ends of the wires and pre-tin them. Solder them onto the LED strips and stick the LED strips on the inside of the roof of the greenhouse.

Make two holes in the roof: one for the toggle switch and one for the cable. The reamer from a Swiss army knife is ideal for this! Pull the USB cable through the lower hole and make a knot in the cable for strain relief.

Mount the toggle switch and solder the USB cable to one set of pins and the 6 leads from the LED strip to the opposing set of pins. Connect and admire the light!

Here are some pictures and a video of the final result. It is still too early to know if it will really help the plants to grow. I’ll post an update as soon as there are some plants to show!