Specifications
| Type | Linear Hall effect sensor, analog output: field strength and polarity, not just present or absent |
|---|---|
| Sensor | Slkor SLSS49E-3, an SS49E-type in a SOT-23 package, under the N/S drawing on the front |
| Output | Half of VCC with no field: 2.5 V at 5 V (2.25 to 2.75 V), about 1.65 V at 3.3 V. Up for one pole, down for the other |
| Sensitivity | 3.25 mV per gauss at 5 V (2.95 to 3.55); about 2.1 mV per gauss at 3.3 V. It scales with VCC |
| Range | A straight line to ±460 gauss at 5 V: 1 V to 4 V. Past that the reading says strong, not how strong |
| Resolution | About 1.5 gauss per count on an Uno or a Pico, about 0.36 on an ESP32 on paper; its ADC jitters by several counts |
| Speed | 3 µs response, typical. 100 nF on SIGNAL makes a filter of 1.3 kHz or more, far faster than a hand-held magnet |
| Supply | Your board's logic voltage on VCC: 3V3 on an ESP32, ESP32-S3 or Pico, 5V on an Uno. The chip runs from 3 to 12 V; from 5 V a strong field takes SIGNAL to about 4 V |
| Current | 3 to 8 mA at 5 V, 5 mA typical, all the time; about 3.3 mA at 3 V. No sleep, no LED |
| Pins to wire | 3 of the 4: GND, VCC and SIGNAL. NC is connected to nothing on the board |
| Header | 4-pin right-angle male, 2.54 mm pitch: GND, VCC, NC, SIGNAL, with GND on the square pad |
| Board | 22.4 × 30.4 mm, two 4.8 mm mounting holes 16 mm apart. The front prints ANALOG, the back MAGNETIC STRENGTH & POLARITY |
| In the box | 1 × TK70 block. It also ships inside the TinkerBlock kits |
What it does
It tells your board how strong a magnetic field is and which way it points. The small black chip under the N and S drawing is an SS49E-type linear Hall sensor. With no field its output sits at half of VCC. A field through the chip moves it by a few millivolts per gauss, up for one pole and down for the other, in a straight line out to about 460 gauss either way.
That makes it the counterpart of the TK18 Hall Effect Sensor, which gives a yes or no from either pole. The TK70 gives the strength and the polarity, which is what MAGNETIC STRENGTH & POLARITY on the back says. Besides the chip there are two 100 nF capacitors, one across its supply and one on its output, and nothing else: no resistor, no LED.
The page this replaces said contactless current sensing starts here, and it does not: a wire carrying 5 A makes about 1 gauss at 1 cm, under one count on an Uno. It also offered either supply as though it suited any board, and said a stronger field means a higher voltage; one pole lowers it.
Two things to know before wiring
- VCC is your board's logic voltage. The output scales with VCC and reaches about 0.8 of it with a strong field: 3V3 on an ESP32, an ESP32-S3 or a Pico, 5V on an Uno.
- Zero field is half scale, not 0. Read SIGNAL with
analogRead, measure the resting value with no magnet near, and subtract it.
Wiring, in four lines
- GND to your board's GND.
- VCC to 3V3 on an ESP32, ESP32-S3 or Pico; 5V on an Uno.
- SIGNAL to an analog pin: GPIO 4 on an ESP32-S3, GPIO 34 on an ESP32, A0 on an Uno, GP26 on a Pico.
- NC to nothing: it is connected to nothing on the board.
Then analogRead(pin) is about half scale with no magnet, and moves up or
down as one comes near.
Where to start
The handbook below is nine short articles, each with a working figure. The first reading is the whole build: it measures its zero and prints gauss with a sign. A pole finder names north or south without flickering.
For how it works, read half the supply at rest and which pole, which way. If the number looks wrong, when the reading is wrong.
When it doesn’t work
- It reads about 512 with no magnet. Is that zero?
- Yes. The output rests at half the supply with no field, which is about 512 of 1023 on an Uno. The field is how far the reading moves from there, up for one pole and down for the other. Chips differ by up to a quarter of a volt at 5 V, so measure your own zero at start-up rather than assume 512.
- Should VCC go to 3V3 or 5V?
- To your board's logic voltage: 3V3 on an ESP32, ESP32-S3 or Pico, 5V on an Uno. From 5 V a strong field takes SIGNAL to about 4 V, more than a 3.3 V pin takes. The chip is specified from 3 V, so 3.3 V is fine.
- Which pole makes the reading go up?
- By the data sheet's drawing for this package, a north pole held over the front. The same pole behind the board makes it go down. The maker's drawings disagree between the chip's two packages, so check once with a compass: the needle's north end points at a magnet's south pole.
- How close does a magnet have to be?
- It depends on the magnet. On paper a 10 × 3 mm neodymium disc, face on, is past the straight part of the range inside about 7 mm and still a few counts on an Uno at about 4 cm. A flat fridge magnet may need to touch the board.
- Can it measure the current in a wire?
- Not on its own. A wire carrying 5 A makes about 1 gauss at 1 cm, under one count on an Uno and about the size of the Earth's field. Current sensors that use a Hall element put the conductor inside the package, like the ACS712, or gather the field with an iron ring round the wire.
- What is the difference from the TK18?
- The TK18 Hall Effect Sensor is a switch: one bit, LOW when a field of either pole passes about 40 gauss, with a light that shows it. The TK70 gives a number: how strong the field is and which way it points, and nothing lights.