Dynamite Sampler Pro

The Dynamite Sampler Pro is a load cell interface with 4-channel, true simultaneous sampling at 1kHz, streamed over BLE.

Extremely low noise floor: 1 gram RMS noise with a 100kg load cell [1]. This is close to the physical limits of what’s possible with an LC. Achieved through our low-noise analog front-end stage. All of this means that you get smooth high-speed derivatives, usable for tasks such as measuring rate of force development.

Extremely tolerant to bad power input. It can withstand 1Vpp noise (0.1Hz-10MHz) and a voltage sag as low as 4V to on the power line with no measurable effect on the signal. Even the cheapest USB adapters with extra-long cables are usable.

Built-in high quality excitation (4.53V).

Open source firmware. https://github.com/K3Engineering/dynamite-sampler-firmware
Open source app. You can test drive it here (no device required) dynamite-app.k3engineering.com 

[1] 350 ohm LC, grounded, 1kHz data, no low pass filtering, not equalized.

Application notes
In our experience, the metal body of the load cell body is electrically insulated from any of the leads in the cable. Notably, on anodized aluminum load cells, the only area that is conductive to the LC body is the threads. This means that if the LC mounting is nonconductive (or the mounting jig itself is not grounded), the LC body is floating regardless of the connection to the LC interface or what the LC interface does.

In case of a floating LC body, the primary form of mains coupling is H-field. In regular use, this mains coupling is detectable via FFT but doesn’t meaningfully affect RMS noise numbers. However, in very close proximity (below 6”) to mains, without mitigation, it can result in very significant signal presence. Given that H-field coupling isn't a traditional grounding loop, galvanic isolation does not help. To mitigate, make sure that the LC body is grounded, either through the jig, or by connecting it to the GND lead. In the Pro model, if planing to use the aluminum case as a grounding point, note that the case itself is anodized.

Given the electrical insulation between the LC bridge and the LC body, ground loops are typically not an issue. However, if they do become an issue, please send us an email so we are aware of the use case. We have tested our interface in the following isolation configurations: 1) powering off a battery (power bank or phone) 2) using a galvanic isolator such as a standard $20 B0505s-1W + ADUM3160 + X USB isolator, or powering off of galvanically-isolated PoE (GPD2CAT-20V in our testing). If you find that your load cell body has conductivity to the leads, we'd love to hear about that as well.

We have also tested our interface in situations such as powering off of a PC USB hub - in which case the signal is typically within the noise spec without any mitigations (floating LC body).

In practice, we see about a 3C rise during the 30-minute warm-up period.