Or, designers can use a relay for loads that exceed switch ratings, especially for applications that feature high current or high voltages such as 120 Vac ( Fig. Other devices with higher ratings can solve the problem for some applications. The PIO pin of that device is limited to 6 V or 4 mA, which restricts the type of load or relay it can drive. By monitoring voltage at its PIO pin, the DS2405 also lets designers read back the state of the load. The load can be connected to the open-drain switch directly, or indirectly through a relay. These are all defined as inline functions, which makes them effectively like macros without needing to use macro syntax.įinally, timing is performed using Timer/Counter1.One-wire switches such as the DS2405 from Maxim Integrated Products allow designers to control remote loads through the versatile one-wire network. You can't explicitly program an ATtiny85 I/O pin as an open-drain output, but fortunately you can achieve the same effect by programming the pin low: PORTB = PORTB & ~(1>OneWirePin & 1 This allows several devices to be connected to the same bus, and pull the bus low simultaneously without a clash. The 1-Wire interface requires each device to connect to the bus using an open-collector or open-drain output. A series of serial EEPROMs, including the DS28EC20 20Kbit serial EEPROM.Īnother feature of 1-Wire is that all devices are programmed with a unique 48-bit serial number in ROM, to allow you to identify multiple devices connected to the same 1-Wire bus.The DS2417 crystal-controlled real-time clock.The DS18B20 and MAX31820 temperature sensors.

The 1-Wire interface was originally developed by Dallas Semiconductor, which was acquired by Maxim Integrated in 2001, and Maxim now make a few interesting devices that communicate by 1-Wire: It's especially useful on processors with a limited number of I/O pins, such as the ATtiny85, as it only uses up one pin. Introductionġ-Wire is an ingenious interface that allows a master device to communicate with one or more slave devices over a single wire (plus ground). I also plan to use it in a couple of project that I'll describe in future articles.

To test it I built a circuit driving a serial 4-digit seven-segment display, displaying temperature using the DS18B20 1-Wire temperature sensor:Ī digital thermometer based on the DS18B20 and a simple 1-Wire interface for the ATtiny85. This article describes a simple 1-Wire interface for the ATtiny85, or other AVR processors.

What is one wire library