Soil Moisture Sensor

[amyCC]

Posted on behalf of student
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I ordered the electronic sensors kit. I want to build the soil moisture sensor and I made sure I followed all the instructions on your website. I made sure nothing is touching each other and the the lightbulb is placed the right way. However, I cannot get the light to turn on. Can you please take a look at the pictures below and tell me what i have done wrong?

Project url: https://www.sciencebuddies.org/science- ... erve-water

20250126_171841.jpg (3.38 MiB) Viewed 6425 times

20250126_171836v2.jpg (1.72 MiB) Viewed 6425 times

[bfinio]

Hi - it's hard to tell from the picture but there's a chance your LED is backwards. The rest of your wiring looks correct. Can you try flipping the LED around and seeing if it works?

You can also confirm that there's nothing wrong with the LED by connecting the 470 ohm resistor directly to the positive (+) bus - remove the leg of the resistor that's currently in hole B3 and move it to the positive bus. The LED should light up. If it doesn't light up, flip the LED around. This tests the LED directly without using the NAND gate. If it STILL doesn't light up, then your circuit does not have power - you may have a dead battery (unlikely with a brand new kit) or the battery snap connector/wires may be loose.

[abdul321]

Thank you for this information. I made sure the led is correctly placed, and when I remove the black wire, it turns on. However, whenever I put the black wire in the breadboard it does not light up anymore.

[bfinio]

Hi - to clarify, do you mean that you have the LED and 47 ohm resistor in their original position, and the LED turns on when you remove the black jumper wire that is connected to row 7?

[abdul321]

Yes

[bfinio]

Ok - do you recall making any mistakes while initially building the circuit, such as reversing the red and black wires from the battery pack or putting things in the wrong bus (+ or -) on the breadboard? As far as I can tell from your photos, your circuit is built correctly, but a previous error could have resulted in damage to the NAND chip such that it is no longer functioning properly.