[Board]: Affordable, portable 1W Meshtastic ready platform with ESP32+OLED+GPS pads (Radiomaster Bandit Nano 900MHz ELRS Module)

[uberhalit]

SOC

ESP32

Lora IC

SX1276

Product Link

https://www.radiomasterrc.com/products/bandit-nano-expresslrs-rf-module

Description

Being a drone racer, I've always wondered if we could turn some ELRS 900MHz gear into a low-cost, reliable, and super powerful Meshtastic device.

By adhering to the ELRS board definitions, I was able to incorporate base support for the model referred to above:

It even features free UART pads that can be utilized to potentially connect a GPS.
Fork available here.
The display requires a flipping in settings.

Nevertheless, currently, neither of the two PAs appears to be engaged, and the power output is below -20dBm. I attempted to hack together a basic 30dbm output PoC, but was unable to do so.

ELRS is calling dacWrite() on pin 26 (power_apc2) and a regular writeRegister to register 0x09 to activate the PAs.
The call to reg 0x09 is already being executed in the current firmware implementation, albeit with different settings.
Manually setting both to the same values as seen in ELRS source does not seem to work, I'd assume that either the SX1276 support is incomplete or a crucial PA initialization is missing (mostly related to RFAMP or LR1121).

In any case, Radiomaster is known for their excellent support. They immediately responded and offered technical help, so this board should come to live eventually.

[RadioMasterRC]

Thanks for your efforts @uberhalit !

If anyone is interested in contributing, we are happy to make hardware available. Reach out to @sachaw on Discord and we can hook you up.

Looking forward to it 💯

Ben.

[dhandzic]

Hmm, the SX1276 supports +20dBm and the LR1121 +22 dBm output. Unless there is an external PA it is hard to see how +30dBm could be achieved. Any information if there is an external PA and how it is controlled or if it is just a fixed gain PA?

[RadioMasterRC]

Hmm, the SX1276 supports +20dBm and the LR1121 +22 dBm output. Unless there is an external PA it is hard to see how +30dBm could be achieved. Any information if there is an external PA and how it is controlled or if it is just a fixed gain PA?

Hi @dhandzic The Bandit Nano uses a Skyworks SKY66122 PA. The PA Voltage is controlled via the ESP32 DAC port and works together with the SX1276 RF power to set the output power. The effective power control range is 100mw - 1000mw

Additional info:
https://github.com/ExpressLRS/ExpressLRS/tree/master/src/lib/POWERMGNT

The Bandit Nano uses the "DACWRITE" function.

[dhandzic]

Hmm, the SX1276 supports +20dBm and the LR1121 +22 dBm output. Unless there is an external PA it is hard to see how +30dBm could be achieved. Any information if there is an external PA and how it is controlled or if it is just a fixed gain PA?

Hi @dhandzic The Bandit Nano uses a Skyworks SKY66122 PA. The PA Voltage is controlled via the ESP32 DAC port and works together with the SX1276 RF power to set the output power. The effective power control range is 100mw - 1000mw

Additional info: https://github.com/ExpressLRS/ExpressLRS/tree/master/src/lib/POWERMGNT

The Bandit Nano uses the "DACWRITE" function.

Thank you for the information. Cool with a +30 dBm node as a repeater. Do you have any figures on the standby current consumption?

[dhandzic]

Hmm, the SX1276 supports +20dBm and the LR1121 +22 dBm output. Unless there is an external PA it is hard to see how +30dBm could be achieved. Any information if there is an external PA and how it is controlled or if it is just a fixed gain PA?

Hi @dhandzic The Bandit Nano uses a Skyworks SKY66122 PA. The PA Voltage is controlled via the ESP32 DAC port and works together with the SX1276 RF power to set the output power. The effective power control range is 100mw - 1000mw

Additional info: https://github.com/ExpressLRS/ExpressLRS/tree/master/src/lib/POWERMGNT

The Bandit Nano uses the "DACWRITE" function.

Could the device be used for 869 MHz too or is the RX filter tuned for 915 MHz?

[uberhalit]

Hmm, the SX1276 supports +20dBm and the LR1121 +22 dBm output. Unless there is an external PA it is hard to see how +30dBm could be achieved. Any information if there is an external PA and how it is controlled or if it is just a fixed gain PA?

Hi @dhandzic The Bandit Nano uses a Skyworks SKY66122 PA. The PA Voltage is controlled via the ESP32 DAC port and works together with the SX1276 RF power to set the output power. The effective power control range is 100mw - 1000mw
Additional info: https://github.com/ExpressLRS/ExpressLRS/tree/master/src/lib/POWERMGNT
The Bandit Nano uses the "DACWRITE" function.

Thank you for the information. Cool with a +30 dBm node as a repeater. Do you have any figures on the standby current consumption?

I measured 2.3W on ELRS while transmitting 30.1dbm and around 0.5W in idle with display on.

Could the device be used for 869 MHz too or is the RX filter tuned for 915 MHz?

You can set it to 868MHz too, that's what I am using it with.

[thebentern]

If somebody wants to add official support for this, we can for sure integrate it, but I'm closing this as an active issue. I don't have the bandwidth to integrate more SX1276 based boards with all of the backlog of devices to support.

[uberhalit]

If somebody wants to add official support for this, we can for sure integrate it, but I'm closing this as an active issue. I don't have the bandwidth to integrate more SX1276 based boards with all of the backlog of devices to support.

Is this subject open to discussion? As far as I am aware, this device should have high priority, as it is the only portable 900MHz device with adequate output power for dense urban environments. I've noticed a lot of interest lately, and the top complaint in YT comments is the poor range in cities without them realizing that their device is limited to 125mW (I guess the 30dbm max output setting is a bit misleading). It would be unfortunate if potential users were to abandon the project because they were unable to obtain a proper link in complex environments.

[gjelsoe]

If somebody wants to add official support for this, we can for sure integrate it, but I'm closing this as an active issue. I don't have the bandwidth to integrate more SX1276 based boards with all of the backlog of devices to support.

Is this subject open to discussion? As far as I am aware, this device should have high priority, as it is the only portable 900MHz device with adequate output power for dense urban environments. I've noticed a lot of interest lately, and the top complaint in YT comments is the poor range in cities without them realizing that their device is limited to 125mW (I guess the 30dbm max output setting is a bit misleading). It would be unfortunate if potential users were to abandon the project because they were unable to obtain a proper link in complex environments.

Are you still working on this?

[thebentern]

it is the only portable 900MHz device with adequate output power for dense urban environments

The G2 station can achieve more power than this radio, and has an SX1262 which features a much more sensitive RX end, which makes a greater difference than raw transmit power in my experience, with multiple A/B tests of SX1262 with RX boosted gain w/ 22dbm TX vs 30dbm setups. I'm afraid 30dbm will not be the silver bullet expectations would have you believe. This is a line of sight technology.