Specification questions

Alec posted Nov 10, 2020:

Hi. I have some questions about the notecard:

1- What is the memory size for the notes queues
2- What is the memory size of the host firmware
3- What is the accuracy of the onboard temperature sensor
4- What is the accuracy of the onboard voltage monitor


@bsatrom posted Nov 11, 2020:

Hey Alec thanks for the question! Let me dig up answers on these and I’ll get back to you.

@bsatrom posted Nov 12, 2020:

@Alec, a few answers for you:

  1. Memory Size for Notes - The Notecard provides approx. 900KB of non-volatile storage for Notefiles. This is cumulative across user Notefiles and the size of an individual file depends on the number of Notes, and whether those are raw JSON notes, or templated notes

  2. Memory Size of Host Firmware - If you are referring to the STM32 processor on the Notecard, that codespace is not developer-accessible, so we don’t disclose the size of the main firmware. If you’re referring to the size of a MCU Host binary that can be downloaded from Notehub to the Notecard, the limit is approx. 700KB.

  3. Accuracy of the onboard temp sensor - For the specifics on this one, I’ll refer you to the datasheet for the LIS2DW12 which we use as both an accelerometer and temperature sensor. And as an additional FYI, the card.wireless request includes a calibration value in the response that indicates the amount we’ve chosen to offset the raw reading based on real-world usage and testing. For example:


The value is the calibration-adjusted temperature, meaning that the sensor reads 3 degrees C higher

  1. Accuracy of onboard voltage monitor - We measure voltage using an ADC with 10-bit resolution. That said, the monitor is pre-calibrated under the assumption that between the supply and the V+ pin there is a single FSV1045V Ultra-Low VF Schottky diode, which we include on all Notecarriers. If you’re building a custom carrier board and need to use a different type of diode with a different forward voltage drop, you can adjust calibration by using the “calibration” argument on card.voltage.

Hi. I cannot find any information about the calibration of the voltage. Is there any documentation?

Hi Alec, I don’t believe there is voltage calibration as such (unlike the card.temp). The card.voltage response from the Notecard is based on the voltage seen by the Notecard at its ADC input and adds the estimated diode drop voltage to account for the protection diodes on the Notecarrier A.

We have made significant improvements to the ADC calibration and the estimation accuracy of the voltage drops on the STPS3H100U (if USB powered) or FSV1045V diodes that are on the Notecarrier A since the most recent developer firmware release (1.5.3) and these will be in our next developer firmware release which is coming quite soon.

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Does release 1.5.5 now include a way to remove the voltage drop ?

If no, is there a static offset that I could apply?


Hi Alec,
1.5.5 adds the estimated diode drop of the STPS3H100U - 0.35v (if USB powered) or FSV1045V diodes ~ 0.2v (if not USB powered) in order to estimate the voltage as seen by the Notecarrier. Are you designing your own Notecarrier and wish to subtract the estimated diode drop ? If you plan on using the Notecarrier in your design you may want to retain these diode drops since they cause card.voltage to show the voltage seen by the Notecarrier.

If you want to remove the diode drop to get the voltage as seen by the Notecard you can use {"req":"card.status"} to check if the Notecard thinks it is connected to USB power (response will contain “usb”:true).

You would then use

{"req":"card.voltage", "set":true, "calibration":<offset>} to set a floating point offset of either -0.2 or -0.35


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