---
name: "owsbm"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/owsbm"
---

# owsbm(4)

1-Wire smart battery monitor device

## NAME

**owsbm** – 1-Wire smart battery monitor device

## SYNOPSIS

**owsbm\* at onewire?**

## DESCRIPTION

The **owsbm** driver provides support for the 1-Wire smart battery monitor. The sensor possesses a temperature sensor, an A/D converter for measuring both battery voltage and current, a current accumulator of both incoming and outgoing current, an elapsed time and 40 bytes of nonvolatile EEPROM.

Only the three voltages (VDD, VAD, CR) and temperature are accessible by the [sysctl(8)](/sysctl/8.md) interface.

The following chips are supported by the driver:

- Maxim/Dallas DS2438

## MEASURING CURRENT

The sensor does not measure current directly. Instead it measures the voltage across the Rsens pins.

```
I = Voltage CR / Rsens    (where Rsens is in Ohms)
```

## SEE ALSO

[intro(4)](/intro/4.md), [onewire(4)](/onewire/4.md), [owtemp(4)](/owtemp/4.md), [sysctl(8)](/sysctl/8.md)

## HISTORY

The **owsbm** driver first appeared in OpenBSD 4.1.

## AUTHORS

The **owsbm** driver was written by Aaron Linville ⟨*aaron@linville.org*⟩.