The Interchangeability of ATtiny Microcontrollers
By Jeremy Cook
When you need a microcontroller that can handle minor tasks with extreme reliability—and with a low BOM cost—the ATtiny85/45/25 family of microcontrollers is a go-to option for many engineers. These devices are notable for their minuscule size, along with limited IO capabilities (5 dedicated IO + reset). They work within a wide voltage range and use very little power. This makes the ATtiny perfect for use in battery-powered emobility devices, or energy efficient appliances where every bit of power counts.
Image: Jeremy Cook
However, with ongoing supply chain issues, it may not be possible to find the exact ATtiny model that you’re accustomed to using, and when you can find what you need, the price may be different than expected. The good news is that there may be an alternative for your newest autonomous machine, smart building technology innovation, or other smart device, in the form of another ATtiny microcontroller. Often one ATtiny can function as a drop-in replacement if the specifications are sufficient.
ATtiny Differences (25/45/85)
Studying the lengthy (234 page) ATtiny25/V / ATtiny45/V / ATtiny85/V datasheet, you’ll find that these little chips are extremely impressive, packing an enormous number of capabilities into a housing that could easily be lost to a vacuum cleaner. You’ll also find that the processing differences between the three lie primarily in their memory configurations. All have standard versions that run at between 0-20 MHz, as well as the low-voltage -V version that runs at 0-10 MHz. They also share the many available peripherals, like PWM outputs, ADC inputs, and touch functionality.
Memory statics can be found on page 1 of the datasheet. Summarizing for the 25, 45, and 85 respectively:
- • Flash: 2/4/8 kilobytes
- • EEPROM: 128/256/512 bytes
- • SRAM: 128/256/512 bytes
Given their common features, if a chip has been over-spec’d memory-wise, for future proofing or other reasons, now may be a good time to reevaluate which processor should be used in a particular device. The ability to be flexible here can help weather any supply interruptions and potentially save costs in the future, depending on microcontroller prices.
ATtiny25/45/85 Packages
In addition to memory needs, for chips to be drop-in replacements for one another their packages must also be compatible. The good news here is that every ATtiny variation is available in the following formats, as described in detail on pages 204-211 of the datasheet:
- • 8P3 – 8-lead Plastic Dual In-line Package (PDIP)
- • 8S2 – 8-lead Plastic Small Outline package (EIAJ SOIC)
- • 20M1 – 20-pad Micro Lead Frame Package (MLF)
Image: Jeremy Cook | .1” header for scale
The ATtiny85 is only available in those (8P3, 8S2, 20M1) formats, meaning that the 25/45 both have a compatible form-factor for any ATtiny85 chip. However, the ATtiny25 and ATtiny45 each have an additional format that is not seen elsewhere in this family:
- • ATtiny45 – 8X – Plastic Thin Shrink Small Outline Package (TSSOP)
- • ATtiny25 – S8S1 – Plastic Gull Wing Small Outline Package (JDEC SOIC)
These devices can also be obtained in a wafer format. While somewhat out of this article’s scope, it’s mentioned for completeness, and may be worth consideration.
Voltage, Processing Speed, and Temperature Tolerance
The ATtiny25/45/85 chips are all available in 10 MHz clock speed “V” versions (e.g. ATtiny25V-10MU), which require power at between 1.8-5.5V. Each is also available in 20 MHz “non-V” versions (e.g. ATtiny25-20MU), which require a slightly higher minimum 2.7-5.5V power supply.
Standard temperature ranges for the ATtiny are between -40ºC and +85ºC. Extended ranges of up to +105ºC and +125ºC are available for the ATtiny25 only.
Other ATtiny Possibilities
Image: Jeremy Cook
The ATtiny25/45/85 is a reliable automation component, and as discussed here, they are cross-compatible in many situations. One might also consider Microchip’s newer 1 and 0-series ATtiny microcontrollers for projects, though using them in an existing design would require a bit more adaptation than simply dropping in another ATtinyx5 chip.
ATtiny Capability Experiments
While the ATtiny series is limited in its uses, it’s quite helpful for certain projects, such as embedded devices that need to accomplish a few simple tasks. For a few ideas on their capabilities, and experiments to get you started with them, see the following articles:
Whichever type of ATtiny you choose–or choose to substitute–you can be assured of extremely dependable processing capabilities in a very small package.
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