Creating a load on a battery using the radio

[JZone]

I am in a need to measure a battery level under a constant load. Rather than adding a custom electronics, I am considering using the radio. I believe there is a way of doing that (see https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/samples/peripheral/radio_test/README.html).

For my use case I need something very simple, that could be embedded in our standard, production software. Would you please advise on the right register configuration ?

nRF52833

SDK 17

[JZone]

Thanks for the response. I need more than that. 10 to 20mA would be ideal.

[JZone]

The test is intended too be executed only during a power-on of the normal application

1. Normal application starts

2. Put radio in TX by a direct configuration of radio registers

3. Measure battery voltage for 1 to 2s

4. Disable radio

4. If battery ok, continue with initialization of the app, start the Soft Device.......

. 

[hmolesworth]

I do something similar for measuring coin cell capacity by monitoring voltage decay under a known load via Bare-metal Radio Transmit. Similar to solar_sensor_beacon sample on the Nordic GitHub repo. The code can be run before nRFConnect stuff if using nRFConnect environment.

solar_sensor_beacon

advertising-using-raw-radio-registers

Edit: I wrote these notes, might be useful if you want to actually have detectable advertising packets. Note also that you can get a fixed load by using Rx instead of Tx if you want to keep the environment cleaner.

// BLE Advertising Packet
// ======================
// Every packet begins with an 8 bit preamble, an alternating binary sequence. This is followed by a 32 bit access
// address (AA) which can be thought of as a unique identifier which defines a particular connection. When a
// device (master or slave) transmits on an advertising channel it uses a fixed value of 0x8e89bed6 as the access
// address.
// Following the 32 bit access address are optional S0, LENGTH and S1 fields then a variable length Protocol Data
// Unit (PDU) which contains the message data payload. Finally all packets end with a 24 bit CRC.
// By default, the Nordic BLE address is derived from the NRF_FICR->DEVICEADDR[] and is 48 bits in length (6 bytes)
// If S0, LENGTH or S1 are specified with zero length their fields will be omitted in memory, otherwise each
// field will be represented as a separate byte, regardless of the number of bits in their on-air counterpart
// For the field sizes defined in bits, the occupation in RAM will always be rounded up to the next full byte size
// (for instance 3 bit length will allocate 1 byte in RAM, 9 bit length will allocate 2 bytes, etc.).
// On-air packet layout (Note Header in RAM is 3 bytes if S0INC is '1')
// +-------------------------------------------------------------------------------------------------------------------------+
// |                                         BLE Advertising Packet - Legacy                                                 |
// +-------------------------------------------------------------------------------------------------------------------------+
// |                                         1MHz: 47 octets max total length                                                |
// +--------+-------+------------------------------------------------------------------------------------------+------+------+
// |        |Access |                                                                                          | Add  |      |
// |Preamble|Address|                   Protocol Data Unit PDU                                                 | On   | CRCC | Tone Ext
// +--------+-------+------------------------------------------------------------------------------------------+------+------+
// |   1(2) |   4   |                                    2 - 39                                                | (0)  |  3   | 16 - 160uSec
// |        |       +-----------------+------------------------------------------------------------------------+      |      |
// |        |       |    Header       |                  Payload                                               |      |      |
// |        |       +-----------------+------------------------------------------------------------------------+      |      |
// |        |       |       2         |                  0 - 37                                                |      |      |
// |        |       +-----+-----+-----+------------------------------------------------------------------------+      |      |
// |        |       | Opt | Opt | Opt |  MAC Addr  |     AdvData List (example 3 fields)                       |      |      |
// |        |       | S0  | Len | S1  +------------+-----------------------------------------------------------+      |      |
// |        |       |-----+-----+-----|    6       |     0 - 31                                                |      |      |
// |        |       | (1) | (1) | (1) |            +-------------------+-------------------+-------------------+      |      |
// |        |       |     |     |     |            |    AdvData Flags  |    AdvData Name   |   (AdvData Data)  |      |      |
// |        |       |     |     |     |            +-------------------+-------------------+-------------------+      |      |
// |        |       |     |     |     |            |        3          |          6        |       0 - 22      |      |      |
// |        |       |     |     |     |            +-----+------+------+-----+------+------+-----+------+------+      |      |
// |        |       |     |     |     |            | Len | Type | Data | Len | Type | Data | Len | Type | Data |      |      |
// |        |       |     |     |     |            +-----+------+------+-----+------+------+-----+------+------+      |      |
// |        |       |     |     |     |            |  1  |  1   |  1   |  1  |  1   |  4   |  1  |  1   |  20  |      |      |
// |        |       |     |     |     |            |     |      |      |     |      |      |     |      |      |      |      |
// |  1(2)  |  4    | (1) | (1) | (1) |   6        |  1  |  1   |  1   |  1  |  1   |  4   |  1  |  1   |  20  | (0)  |  3   |
// +--------+-------+-----+-----+-----+------------+-----+------+------+-----+------+------+-----+------+------+------+------+
//         0x8E89BED6     |     |      \
//                /       |     |       \
//               /  RAM uses 2+ bytes    \
//              / 1 byte | 2 bit | 6 bit  \
//             /                           \
//            /  OTA only 2 bytes for BLE   \
//           |                         |     |
//           Type RFU ChSet TxAdd RxAdd Length
//    bits:    4   1    1     1     1     8

[hmolesworth]

Continuous Rx until advertising packet received (then restart Rx) with HFCLK crystal enabled I see 8.8mA @3V on nRF52832 with no DC-DC, no hardware attached to io pins and no peripherals enabled.

[JZone]

Thanks for the suggestions. The following solution seems to work

NRF_RADIO->MODE = 0; // 1 Mbps Nordic proprietary radio mode
NRF_RADIO->TXPOWER = 0x08; // +8dBm
NRF_RADIO->TASKS_TXEN = 1;

test_battery();

NRF_RADIO->TXPOWER = 0; // Set back to default

NRF_RADIO->TASKS_DISABLE = 1;

[hmolesworth]

Excellent suggestion. There is no +8dBm option on the nrf52832 (which I ran this test on) and I see these results @3V on nRF52832 with cpu awake, no DC-DC, no hardware attached to io pins and no peripherals enabled.

23mA at +4dBm is most useful for a faster battery test.

  NRF_RADIO->TXPOWER = 0x08; // +8dBm 11.35mA
  NRF_RADIO->TXPOWER = 0x04; // +4dBm 23.17mA
  NRF_RADIO->TXPOWER = 0x00; //  0dBm 17.42mA