HL7800 Power Saving, 3 wire UART

IoT Modules HL78
1

In process now to try to optimize the HL7 low power modes but having difficulty ever getting there.
The Microprocessor to the HL700 is connected with a 3 wire UART connection.
But it seems that some power setting modes are dependant on the DTR pin.
Though we try to configure +KSLEEP mode to be in standalone mode and using some sample edrx commands found in the HL7800 Low Power Modes Application Note, we can never achieve anything close to low power. We find that our board always consumes around 130mA, turning off the radios with CFUN we can get it down to 60mA.

Is it recommended to not use a 3 wire UART?
If the HL7800 never gets associated with a cell tower, will it prevent it from going into low power mode? I’m asking because currently, our prototype is in a room where no cell connection can be made.

Any guidance is appreciated.

2

Hi Rique,

Some rework is needed to get the low current cosumption:

Dev-kit PCB #5303247 Rev 4:

  • CN1301 and CN302 are open.
  • De-solder R1302.

Follow these steps to check current leakage:

  • Set SW203 OFF.
  • Set SW202 OFF.
  • Set SW1300 OFF.
  • Set SW600 OFF.
  • Set SW500 to USB1.
  • Set SW1400 to USB0.
  • Open CN804.
  • Supply 3.7V to CN800 (supply to the Development Kit).
  • Supply 3.7V to CN801 (supply to the module).
  • Connect the USB cable between CN400 of the Development Kit and a computer.
  • Send AT+CPOF to the module
3

These are for the mangOH board

We have our own prototype built. Any suggestions there?

I’m especially curious about the DTR signal

As well

-Henrique Reis

Reis Information Systems

4

For 2-wired UART (TX/RX), HW flow control will be impossible.
to config eDrx Hibernate mode, you can set:
AT+CEDRXS=1,4,5 //CATM1-81.92s
AT+KSLEEP=1,2 //Standalone-Hibernate

After module enters hibernate(not depending on DTR), you can set WakeupPin=high to force it wake up.

5

We are finally getting around to doing proper power testing on our own board. Using the commands you provided, we do see that the HL7800 will go into low power mode and draw just a few microamps but, it will only do so for a few seconds. It will then wake up (even though we did not assert WAKEUP), and it will begin to draw alot of power. Any ideas what is happening here or how to begin to figure it out?

6

Normally it needs ~10 minutes to do RTC calibration after start up. So you need to wait longer time.
Please refer to the appliation note.
AirPrime_HL7800_Low_Power_Modes_Application_Note_Rev2_0.pdf (627.3 KB)