麻豆传媒

YOU have gone seven days with a moody plant after we left it complaining last week. Now we can give it both the means and a reason to be happy.

First, tweak your code to show a smiley face when the plant鈥檚 conditions are good. Open your code in the editor 鈥� now the variables we created last week will come in handy. Take another 鈥渋f鈥� block with no 鈥渆lse鈥� part, and snap it under the first two. Then slot in a 鈥淺<\> and \<\>鈥� block from the 鈥淟ogic鈥� menu, and two 鈥�0 = 0鈥� comparisons. Slot the 鈥�0 = 0鈥� blocks either side of 鈥渁nd鈥�.

Next, take your variables, DRY and WRONG TEMP, as well as two 鈥渇alse鈥� blocks from the 鈥淟ogic鈥� menu and make a line that says 鈥渋f DRY = false and WRONG TEMP = false鈥�. Nestle a 鈥渟how icon鈥� from 鈥淏asic鈥� inside the 鈥渋f鈥� block and select the smiling face.

Now it is time to build an automatic waterer to stop your plant drying out. For this we need a transistor. A transistor can act like an electronic switch. It has three legs, two of which are connected or not depending on the current going into the third.

Grab your breadboard (for a refresher, see 鈥淗ow to be a maker鈥�, 25 May), and place the transistor so its legs each sit in different rows. Connect the middle leg, called the 鈥済ate鈥�, to pin 1 on the micro:bit. On my transistor, when the flat side is facing me, the right leg is the 鈥渄rain鈥� and the left is the 鈥渟ource鈥�. Yours will probably be the same, but check the packet to be sure. Connect the drain to the pump鈥檚 ground wire, which should be white, and the source to micro:bit鈥檚 ground. Connect the pump鈥檚 red power wire to micro:bit鈥檚 3v pin.

Now, when the micro:bit sends a 1 to the transistor鈥檚 middle leg, it will complete the circuit, while a 0 will break it. This lets us switch the pump on and off.

Let鈥檚 add to our code to do this. From the 鈥淧ins鈥� menu, grab a 鈥渄igital write pin鈥� and select P1 from the drop-down. Leave the 0 at the end and clip the block into 鈥渙n start鈥�. This will make sure that the pump is off to begin with.

Next, under the block that says 鈥渟et DRY to true鈥�, add another 鈥渄igital write pin p1鈥�, but this time change the 0 to a 1. Underneath that, slot in a 鈥減ause鈥� from 鈥淏asic鈥� and select 2 seconds from the drop-down. Add another 鈥渄igital write pin p1鈥� underneath, leaving the 0 in the box. This will switch on the pump for 2 seconds then off again when the soil is dry. Add one final 鈥減ause鈥� below, typing in 10,000. This makes the system wait 10 seconds for the water to percolate. Once again, if you get stuck, online.

Finally, put the pump in a bowl of water and attach a length of tube between it and the plant pot. And you鈥檙e done! Now you can go on holiday and return to a happy houseplant.

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New stuff you need

For next week

Old smartphone

Phone stand

Next in the series

1 Moisture-sensing plant

2 Moisture and temperature-sensing plant

3 Plant auto-waterer

4 Tweeting wildlife camA motion-controlled animal spotter

5 Pest scarer

6 BBQ thermometer

7 Rain alarm

8 Mini weather station

9 Remote controlled pest-proof bird feeder part 1

10 Remote controlled pest-proof bird feeder part 2

Email: maker@newscientist.com