Weston Braun
Test Equipment
KiCad
Little Bee
An affordable, high-performance current & magnetic field probe
Weston Braun
Test Equipment
KiCad
The behavior of an electronic device is determined by both voltages and currents. Measuring voltages with an oscilloscope is easy, but current probes are expensive enough to be out of reach for many people. Little Bee is an affordable and high performance current probe and magnetic field probe that will allow you to debug and analyze electronic devices more effectively.
Current probes are especially important for power electronics, which is of rising importance due to electric vehicles, alternative energy, and high-efficiency power supplies. We hope to make the world of power electronics accessible to more people by delivering a much needed piece of test equipment as open hardware and at an affordable price.
Little Bee can be used as a sensitive magnetic field (B Field) probe. Unlike normal current probes, B field probes allow for the non-intrusive measurement of current flowing through PCB traces and inductors by measuring the magnetic fields they generate. While non-intrusive current sensing does not measure an exact current amplitude, it does allow you to quickly verify circuit waveforms and identify faults and short circuits.
Below is a photograph of a sample application in which we use Little Bee to measure the stray magnetic field of a PCB-mount DC/DC converter, providing a waveform proportional to the inductor current.
With the included current sensing attachment, Little Bee functions as a traditional current probe and provides isolated measurements of the current in a wire with higher accuracy. It can measure currents over a wide bandwidth: from DC to the MHz range. Below is a photograph of a sample application in which we use Little Bee to measure the input current to an AC-powered switch-mode power supply.
Little Bee is based on an Anisotropic Magneto-Resistive (AMR) magnetic sensor, which gives it performance comparable to current probes based on fluxgate magnetometers and those with hybrid approaches that couple AC current transformers with DC hall effect sensors. But it offers that level of performance at a much lower cost.
The AMR sensor natively senses magnetic fields, producing a voltage proportional to the magnetic field strength. The clip on current sensing attachment enables current sensing by translating the current in a wire into a magnetic field. It consists of a ferrite toroid with an air gap in which the sensor tip rests. The relationship between the current in the wire and the magnetic field in the air gap varies little as the wire moves around the center of the toroid, providing for accurate current sensing despite variations in the test setup.
The output of the AMR sensor is amplified by a low noise, high bandwidth amplifier to provide the correct signal level for oscilloscopes. The amplifier is controlled by a PIC microcontroller, enabling automatic zeroing and offset adjustment as well as gain and bandwidth switching.
It is important that the open source community have access to high-quality tools. A desire to make a once prohibitively expensive technology accessible to a wider audience inspired the creation of the Little Bee. All the project files are hosted on GitHub under the Creative Commons Attribution-ShareAlike 4.0 license.
| Little Bee B1 | I-prober 520 | Micsig CP2100B | Tektronix TCP2020 | |
|---|---|---|---|---|
| Power Source | AA battery | AC adapter | USB | AC adapter |
| Price | $149 | $795 | $370 | $2,960 |
| Bandwidth | DC - 10 MHz | DC - 5 MHz | DC - 2 MHz | DC - 50 MHz |
| Maximum Current | ±5 A | ±10 A | ±100 A | ±20 A RMS (±100 A Peak) |
| Sensitivity | 0.25 V/A | 1 V/A | 0.1 V/A | 0.1 V/A |
| Noise Level | 3 mA RMS | 6 mA RMS | 4.5 mA RMS | 1 mA RMS |
| Field Measurement Capability | Yes | Yes | No | No |
| Auto Zero Capability | Yes | No | Yes | No |
| Open Source | HW & SW | No | No | No |
Little Bee connects to any oscilloscope with a standard 1 MΩ input impedance by way of the provided SMA to BNC cable. It’s ready for use as soon as you flip the power switch. Its two buttons are used to zero the probe and to cycle through bandwidth and gain options. Full operating instructions, schematics, and source code are available on GitHub.
The main Little Bee PCB will be assembled by MacroFab in the United States, and the mechanical parts will be 3D printed out of Multijet FusionPA12 by Sculpteo. The final mechanical assembly of the probe, firmware flashing, and calibration, will be done in house before shipping all finished units to Crowd Supply’s fulfillment partner, Mouser Electronics.
After testing and packaging all Little Bee products, we will send them on to Crowd Supply’s fulfillment partner, Mouser Electronics, who will distribute them to backers. You can learn more about Crowd Supply’s fulfillment service under Ordering, Paying, and Shipping in their guide. And please remember to keep the shipping address listed in your Crowd Supply account up to date!
Because it is covered by CE requirements, the Little Bee B1 cannot be shipped to EU countries, the UK, Norway, Iceland, or Liechtenstein. Sorry! Depending on interest, we may launch a global, follow-up campaign for a CE-certified version of Little Bee.
We have perfected the electrical design of the Little Bee B1 over a series of five prototypes, and the remaining risks all pertain to manufacturing. The biggest risk for small scale electronics productions is component availability. For example, the Honeywell HMC1041Z magnetic sensor used for Little Bee is currently out of stock at every electronics distributor and is only available as a reel of 3000 with a 16 week lead time. We have spoken with Honeywell directly, however, and they are willing to supply sensors for the project. If that arrangement falls through, we will need to track down a third-party vendor or push back our delivery estimate.
"Current probes are cool but pricey at times. In walks an alternative − Little Bee, a low-cost, high-performance current and magnetic field probe from Weston Braun that's capable of effectively debugging and analyzing electronic devices"
"Little Bee es una sonda para la medición de corriente que viene a solucionar un problema recurrente en el uso de un osciloscopio para la medición de voltajes: el alto coste de las sondas específicas para este propósito"
"Current probes are gaining ground today because of the popularity of power electronics like electric vehicles, alternative energy, and high-efficiency power supplies."
Produced by Weston Braun in Palo Alto, CA.
Sold and shipped by Crowd Supply.
One Little Bee B1 Current Probe. Includes the current sensing attachment and an SMA-BNC cable for connecting to an oscilloscope.
