START A BITParts · Sensors
Ultrasonic sensor for 3.3 V (HC-SR04P)
HC-SR04P, also sold as HC-SR04 2020/2021, 3-5.5 V
Looks like the HC-SR04, often with the same print, but it also works on 3.3 V. Its Echo is as high as its power.
2Use it
| Pin or leg | What it is for |
|---|---|
| VCC | 5 V (the class rule), or 3.3 V from the 3.3 V regulator |
| Trig | a Micro:bit pin, e.g. P1: straight |
| Echo | a Micro:bit pin, e.g. P2: through the divider on 5 V, straight on 3.3 V |
| GND | GND |
- Class rule, for every HC-SR04 of both kinds: VCC to 5 V, and Echo through the divider (1 kΩ from Echo to the pin, 2 kΩ from the pin to GND) or a level converter. Then you never need to know which kind you have.
- On 3.3 V its Echo is 3.3 V: then it may go straight to a Micro:bit pin. On 5 V, Echo is 5 V again and needs the divider.
- For 3.3 V, use the 3.3 V regulator on the USB power board's 5 V. A Micro:bit on its battery pack gives only about 2.8-3 V on 3V: some boards then stop.
- Which kind is it? Power it from the Micro:bit's 3V, Echo straight to a pin. Measure a wall at about 1 m and 2 m, ten times each.
- Steady, right numbers at both: a 3.3 V board. A classic one gives short, odd or no numbers. The test harms neither the sensor nor the Micro:bit.
- Then check the back (the picture): an RCWL or CS100A chip, no 16-pin MAX232. No silver crystal on the front is a good hint too, but not proof. Mark it with a coloured sticker or a dot of paint, and keep it in its own box.
- A marked 3.3 V board can also plug onto the Simple Servo board's P0-P2, 3V and GND pads: no breadboard, no divider.
- Read it with the sonar extension in MakeCode, like the HC-SR04.
Good to know: Sellers often print "HC-SR04" on the front, the same as on the classic one: look at the back. Kitronik's 46114 was this kind, but it is discontinued and its datasheet is the one of the classic HC-SR04.
The idea behind it, step by step: Ultrasonic distance sensor
Used in
No project uses it yet.
3Facts
| Power | 3-5.5 V (some 2.8-5.5 V), about 2-3 mA |
|---|---|
| Range | about 2-400 cm on 5 V, a bit shorter on 3.3 V |
| Echo | as high as its power: 3.3 V on 3.3 V, 5 V on 5 V |
| On the back | an RCWL chip (RCWL-9206, RCWL-9300, RCWL-9610) or a CS100A, no 16-pin MAX232; often M1 and M2 pads; sometimes "+" or "2021" |
| On the front | often no crystal (the RCWL chip has its own clock); some boards have one: a hint, not proof |
Kinds you may find
| HC-SR04 (classic) | 5 V only; three chips on the back, one a 16-pin MAX232 (or no name) |
|---|---|
| HC-SR04+ (4tronix) | the same 3-5.5 V kind |
| Kitronik 46114 | a 3.3 V-tolerant board sold before; Kitronik lists it as discontinued |
More to read
- Fred's Cave: the HC-SR04P ↗
- Mischianti: HC-SR04 and its 3.3 V versions ↗
- Toit: an ultrasonic sensor on 3.3 V ↗