Circuits I — sensing and inputs

A sensor is only useful if the controller can read it — and how it connects depends on the sensor. Knowing the handful of patterns lets you predict what any product needs.

The main ways a sensor talks to the brain:

• Analog — the sensor outputs a varying voltage the controller reads on an ADC pin. Examples in the library: the capacitive soil-moisture probe, and current sensing with an ACS712.
• Digital single-wire — the sensor sends a digital reading over one data line. The DHT22 (temp + humidity) and the DS18B20 (temperature, on a "1-Wire" bus) work this way.
• Timing / echo — the controller sends a pulse and times the return. The HC-SR04 ultrasonic distance sensor does this.
• Interrupt — the sensor just yanks a pin high when something happens, waking the controller. The PIR motion sensor is the classic.
• Amplified / bridge — tiny signals need a dedicated amplifier chip first. A load cell uses the HX711 to turn a faint strain signal into a clean digital reading.

You don't wire these by hand — but recognising the pattern tells you why Forge picks a particular block, and whether your idea is a one-wire job or needs an amplifier.

Let's match a few real products to the sensing block they need — the kind of call you'll make constantly:

Notice the pattern: the thing you want to sense points straight at a block. When you describe a product to Forge, naming the quantity ("soil moisture," "weight," "distance") is usually enough for it to pick the right sensing subcircuit.

Time to compose one. A soil-moisture alarm is a clean input → brain → output product: sense how dry the soil is, and warn when it crosses a line.

Send the prompt and watch Forge pick a capacitive soil-moisture probe (an analog sensing block), read it on an ADC pin, and drive a buzzer + LED as the output.

As you read, notice it's just blocks from the shelf you learned this lesson — connected correctly for you.