# Pololu Romi Encoder Pair Kit 12 CPR

> Pololu #3542 Romi encoder pair kit: two dual-channel Hall sensor boards + two 6-pole magnetic discs for the Romi chassis mini plastic gearmotors, 12 counts per motor-shaft revolution (~1440 per wheel revolution), 3.5–18 V, open-drain A/B outputs (external pull-ups), 20 × 18.7 mm, 0.1″ pads with low-profile headers.

- Manufacturer: Pololu
- Part number: 3542
- Category: Encoders
- Canonical page: https://www.xirkit.io/products/pololu-romi-encoder-pair-kit-12-cpr-1257
- Pinout: https://www.xirkit.io/products/pololu-romi-encoder-pair-kit-12-cpr-1257/pinout
- Structured JSON: https://www.xirkit.io/products/pololu-romi-encoder-pair-kit-12-cpr-1257/data.json
- Source: Xirkit structured parts catalog — every value traced to a cited document; unknowns are explicit.

## Key specifications

| Property | Value |
| --- | --- |
| Sensing | magnetic |
| Type | incremental |
| Resolution | 12 CPR |
| Channels | A/B quadrature |
| Interface | quadrature |
| Output | open-drain digital; pull up externally to your logic voltage |
| Index channel | no |
| Mounting | soldered to the back of a Romi mini plastic gearmotor with extended back shaft; disc pressed on the shaft |
| Supply voltage | 3.5–18 V |
| Dimensions | 20 × 18.7 × 5 mm |
| Certifications | RoHS 3 |

## Pinout (6 pins, 0 with electrical limits)

| Pin | Position | Kind | Chip pad | Functions | VIH | VIL | VOH | VOL | IOH | IOL | 5 V tolerant |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| M1 | JP1 · JP1-1 | motor terminal | — | m1 | — | — | — | — | — | — | — |
| M2 | JP1 · JP1-2 | motor terminal | — | m2 | — | — | — | — | — | — | — |
| VCC | JP1 · JP1-3 | power in | — | power_in | — | — | — | — | — | — | — |
| A | JP1 · JP1-4 | signal a | — | a | — | — | — | — | — | — | — |
| B | JP1 · JP1-5 | signal b | — | b | — | — | — | — | — | — | — |
| GND | JP1 · JP1-6 | ground | — | ground | — | — | — | — | — | — | — |

## Where to buy

| Supplier | Price | Stock | Checked | URL |
| --- | --- | --- | --- | --- |
| www.pololu.com | 9.95 USD | in_stock | 2026-09-29 | https://www.pololu.com/product/3542 |

## FAQ

**What voltage powers the Pololu Romi Encoder Pair Kit 12 CPR?**

Supply range 3.5–18 V.

**How much does the Pololu Romi Encoder Pair Kit 12 CPR cost?**

From $9.95 at www.pololu.com. Prices are observed unit prices before tax and shipping.

**What are the Pololu Romi Encoder Pair Kit 12 CPR dimensions?**

20 × 18.7 × 5 mm. A STEP model is available for enclosure fit checks.

**Where does this Pololu Romi Encoder Pair Kit 12 CPR data come from?**

Every value in this record is traced to a source — 2 documents including the board and chip datasheets — with the page and table cited per value. Unknowns are left explicit, never guessed.

## Sources

- [Pololu Romi Encoder Pair Kit 12 CPR datasheet](https://www.pololu.com/file/0J1208/romi-encoder-pair-kit-schematic-diagram.pdf)
- [www.pololu.com listing](https://www.pololu.com/product/3542)

## Part graph

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- [Pololu Magnetic Encoder Kit 12 CPR (Micro)](https://www.xirkit.io/products/pololu-magnetic-encoder-kit-12-cpr-micro-18c6) — Both serve mobile robot drive trains — check the trade-offs; $9.95 vs $9.95
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