Logger Hardware: Dedicated, Embedded and Industrial
Commercial loggers, microcontrollers with SD, Raspberry Pi, PLC trends and polling devices over a network, with power, enclosure and runtime.
The main options
| Option | Typical cost | Strengths | Limits |
|---|---|---|---|
| Commercial standalone logger (HOBO, Onset, Lascar, Tinytag) | $50 to $500 | Calibrated, sealed, long battery life, software included, fast to deploy | Fixed channels; closed software; limited rate and formats |
| USB or bench DAQ (LabJack, NI, Measurement Computing) | $150 to $5 000 | Many channels, good converters, synchronized sampling, drivers in Python and LabVIEW | Needs a computer connected; not for long unattended use |
| Microcontroller + SD (Arduino, ESP32, STM32, Teensy) | $10 to $60 | Cheap, flexible, low power, timer-accurate | You write and maintain the firmware; hardware design for signal conditioning |
| Raspberry Pi / single-board computer | $40 to $150 | A full operating system, Python, networking, databases, cameras | Less real-time; SD card wear; more power; needs a proper shutdown |
| PLC / industrial controller trend | Already installed | Robust industrial I/O, scan-synchronous, in the plant already | Limited storage and rate; export is awkward; keep logging separate from control |
| Industrial IoT gateway / edge device | $200 to $2 000 | Reads Modbus, OPC UA and others; buffers; sends to the cloud | License and configuration; vendor lock-in |
| Smart sensor / LoRa / BLE node | $20 to $200 | Wireless, battery powered, built-in sensor | Low rate; range and network infrastructure; firmware updates |
- Buy, do not build, when a commercial logger meets the need: your time is usually the biggest cost (see Planning a Logging System).
- Build when you need a particular sensor, rate, trigger or integration, or you need hundreds cheaply.
- Separate logging from control where you can: a logger that reads a machine must not be able to disturb it, and a fault in logging must not stop production.
Dedicated data loggers
| Check | Why it matters |
|---|---|
| Channels and input types | Thermocouple types, RTD, 4–20 mA, voltage, pulse, switch; whether inputs are isolated |
| Resolution, accuracy and calibration | A 12-bit logger and a 24-bit logger differ greatly; look for a calibration certificate (see Sensors, Signal Conditioning and ADCs) |
| Sample rate and memory | Samples at the rate you want, for the duration you want, without overwriting |
| Battery life and power options | Replaceable cells; external supply; alarm for low battery |
| Environmental rating | IP67 or better outdoors; the temperature range of the electronics and the battery |
| Download and software | USB, Bluetooth, Wi-Fi or cloud; export to CSV; no recurring license |
| Alarms and display | Local alarm, LED or email for limits |
Microcontroller loggers
A microcontroller board with an ADC, a real-time clock, an SD card and a battery is the standard home-built logger. Its strengths are timing (hardware timers sample on the microsecond) and very low sleep current. Details of the peripherals, interrupts and power modes are in Embedded Systems.
| Block | Typical part | Notes |
|---|---|---|
| Processor | ESP32 (Wi-Fi/BLE), RP2040, STM32L4 (low power), Teensy 4 (fast), ATmega328 | Choose by peripherals, power and the tools you know |
| ADC | Internal 12-bit, or ADS1115 (16-bit), ADS1256 (24-bit), MCP3564 | External for accuracy and noise; see Sensors, Signal Conditioning and ADCs |
| Clock | DS3231 (TCXO), PCF8523 | Battery-backed; see Time Stamps and Clocks |
| Storage | microSD (SPI or SDIO), FRAM, serial flash | See Storage, Formats and Data Rates |
| Power | Li-ion + charger, 3×AA + buck/boost, mains adapter | Brown-out protection and a supercapacitor for clean shutdown |
| Connectivity | Wi-Fi, LoRa, cellular modem, RS-485 | See Telemetry, Databases and Dashboards |
Worked example: battery life of a one-minute logger
- The logger wakes once every 60 s, draws 45 mA for 0.5 s (reading, writing, radio off), and sleeps at 0.02 mA.
- Average current: (45 × 0.5 + 0.02 × 59.5) ÷ 60 = 0.39 mA (a duty cycle of 0.8 %).
- A 2 400 mAh pack with 80 % usable lasts 2 400 × 0.8 ÷ 0.39 = 4 863 h = 203 days (about 6.7 months).
- The sleep current dominates a duty-cycled design. A regulator with 1 mA quiescent current alone would draw more than the whole logger on average: choose parts with microamp quiescent current.
- Hold-up for a clean shutdown. A 1.0 F supercapacitor falling from 5.0 V to 3.0 V supplies 80 mA for C ΔV ÷ I = 25 s, plenty to finish a write.
Raspberry Pi and single-board computers
- Strengths: Python and pandas on the logger itself, a real database, web dashboard, camera, USB devices, remote login.
- No real-time guarantees: Linux is not hard real time, so sample the fast signal with an external ADC or microcontroller that buffers and sends blocks (see Time Stamps and Clocks).
- No analog inputs: add an ADC board (ADS1115, MCP3008) or read sensors over I²C, SPI, 1-Wire or USB.
- SD card wear and corruption: log to a USB SSD, use a read-only root file system with a writable data partition, shut down cleanly (a small UPS board helps).
- No battery-backed clock: add an RTC, or the Pi restarts with the time of the last shutdown until NTP responds.
- Power: typically 3 W, 600 mA at 5 V: the same 2 400 mAh Li-ion pack (3.7 V) lasts only about 2.4 hours, which is why battery sites use a microcontroller and a Pi is for mains or a solar panel.
PLCs, DAQ and polling devices
Many machines already measure what you want. A PLC, drive, meter or instrument can often be polled over the network (Modbus, OPC UA, EtherNet/IP) by a separate logger, with no extra sensors and no change to the control program (see Industrial Communication).
Worked example: polling time
Reading 200 separate registers one at a time at 10 ms each takes 200 × 10 ms = 2.0 s, so the whole set cannot be refreshed faster than every 2.0 s, and the readings are not simultaneous. Reading blocks of consecutive registers in one request (up to 125) takes a fraction of this. Stamp each batch on arrival, and say that the rate is limited by the poll.
- Use the PLC’s own trend or historian for slow process data when it exists, but export it regularly; PLC memory is small and rolls over.
- Do not poll aggressively: a busy bus slows the control. Use read-only access and ask the controls engineer first.
- Scan-synchronous data (taken in the PLC program, once per scan) is consistent between channels; polled data is not.
- DAQ cards and modules (4–20 mA, thermocouple, RTD inputs on Modbus or USB) turn a PC or Pi into a multi-channel logger.
- Safety: a logger that connects to a control network is part of that network’s security (see Telemetry, Databases and Dashboards).
Power, runtime and solar
| Source | Good for | Watch out for |
|---|---|---|
| Primary lithium cells (AA, D, CR) | Years at microamp averages; cold weather | Cannot be recharged; check the pulse current |
| Alkaline | Cheap, widely available | Poor in the cold; voltage falls through life |
| Li-ion / LiFePO4 | Rechargeable; with solar | Temperature limits for charging (not below 0 °C); a protection circuit |
| Mains adapter + backup cell | Permanent sites | Surge protection; a supercapacitor or battery for shutdown |
| Solar panel + battery | Remote sites | Sized for the worst season (see below) |
| Loop power (4–20 mA) | A sensor-powered node | Only a few mA available |
Worked example: a small solar logger
- The site load is 0.35 W (a cellular modem and logger), so it uses 0.35 × 24 = 8.4 Wh a day.
- With 3.0 peak-sun hours in winter and 60 % system efficiency, the panel must deliver 8.4 ÷ (3.0 × 0.6) = 4.7 W; fit a 10 W panel, which also copes with dirt and shading.
- For 3 days of cloud, using only half of a lead-acid battery, store 8.4 × 3 ÷ 0.5 = 50 Wh (about 4.2 Ah at 12 V).
Enclosure, mounting and environment
- Ingress protection: IP65 sprays; IP67 temporary immersion. Use cable glands rated for the cable, and drip loops so that water runs off.
- Condensation: temperature cycling pumps humid air into an enclosure; fit a breather (a vent membrane) and a desiccant pack, and conformally coat the board.
- Temperature: check the electronics, the battery and the display ranges; Li-ion cannot charge below freezing; a black enclosure in sun runs 20 °C or more over ambient.
- Sensors outside: radiation shields for air temperature (in sunshine a bare sensor reads high), and sensor cables with UV-resistant jackets.
- Lightning and surge: protect long cables and mains with surge arresters, and bond the shield and the frame correctly (see Electronics Fundamentals).
- Vibration and shock: secure connectors; use locking connectors and strain relief; foam or a mount isolates fragile parts.
- Access: a label with the logger ID, an owner and a contact; a way to read it without opening the enclosure.
Choosing and comparing
| If you need… | Start with |
|---|---|
| a few temperature points for a month, with a certificate | A commercial standalone logger |
| many channels at high rates, in a lab | A DAQ module with Python or LabVIEW |
| a cheap, custom, battery-powered sensor node | A microcontroller, a real-time clock and an SD card |
| data processed on site, a database and a dashboard, mains power | A Raspberry Pi with a USB SSD and an RTC |
| data from an existing machine | Poll the PLC, drive or meter over Modbus or OPC UA with a gateway |
| about 12 channels from a 4-channel logger | 3 loggers, with a common marker to align their time (see Time Stamps and Clocks) |
| a remote site with no power | Solar + battery + a low-power microcontroller + cellular or LoRa |
Related
- Data Logging: the overview of this guide.
- Planning a Logging System: working out what the logger must do first.
- Telemetry, Databases and Dashboards: getting data off the logger.
- Embedded Systems and Electronics Fundamentals: the circuits and firmware.
- Industrial Communication: polling PLCs and drives.
FAQ
Should I buy a logger or build one?
Buy if a commercial logger covers the channels, rate and duration: it comes calibrated and tested. Build when you need an unusual sensor, rate or integration, or many cheap units.
Can a Raspberry Pi be a data logger?
Yes, for mains or solar sites with network, databases and Python, using an external ADC and an RTC. It is not a good fit for battery sites or for hard real-time sampling.
How do I make a battery logger last a year?
Sleep most of the time at microamps, wake briefly to sample and write, keep the radio off except to upload, and choose parts for low quiescent current. Compute the average current and the capacity.
Is it safe to connect a logger to a PLC?
Usually if it is read-only, polled gently and on an agreed network segment, with the controls engineer informed. A logger must never be able to write to the control system.
References
- Manufacturers’ logger datasheets (Onset HOBO, Lascar, LabJack, National Instruments); Raspberry Pi and Espressif hardware documentation.
- IEC 60529 (IP codes); IEC 61000-4-5 (surge immunity); battery manufacturers’ datasheets for capacity and temperature derating.
- Horowitz, P. and Hill, W., The Art of Electronics (power, ADCs and low-power design).
Last reviewed: October 2026. Costs and currents are typical: use the datasheets for your parts.