Using transistor with GPIO to switch another chip

[PKSHER]

Hello

I am using pin 1.15 of nrf52840 dongle with transistor with enable pin of another chip. The other chip is a wifi chip which I only want to switch on whenever I have data to send to that chip.

My software design is like this, switch on the chip, send the data and switch off the chip.

I have used a transistor circuit whose base pin when connected to high (3.3V), switches on the wifi chip and when connects to low (0V) switches it off. But when I try to do the same with the dongle, it is not working. The dongle is not able to supply 3.3V when connected to the transistor circuit, and when I disconnect the circuit, it supllies 3.3V. This may be related to current but I am using 10K base resistor. I am attached the picture for your reference.

I appreciate your suggestions.

Regards,

[Dmitry]

AFAIK esp32 board has an internall pull-up on EN pin (oops.. we don't know what board you have..)

I can see two cases:

- your esp32 board is not powered at all, and it tries to get parasite power from EN pin

- your board is held in reset by internal cirquitry (DTR=1 RTS=0 causes that)

[PKSHER]

I want to use nrf gpio to switch esp32 on and off. How can I achieve this. I connected gpio with transistor to drive esp32 enable pin high and low but could not achieve anything. Plus there is another issue that is related to this, that when my esp32 is off, the nrf dongle does not work either, I donot know why?

[Dmitry]

I think you should check all power and ground connections. It seems that your dongle gets power from P0.31.

[PKSHER]

I have figured it out. Actually its uart flowcontrol issue. When I define uart as following, it does not work, although I am disabling it. 

static void uart_init(void) {
  uint32_t err_code;

  bsp_board_init(BSP_INIT_LEDS);

  const app_uart_comm_params_t comm_params =
  {
    31,
    29,
    6,
    8,
    APP_UART_FLOW_CONTROL_DISABLED,
    false,
#if defined(UART_PRESENT)
    NRF_UART_BAUDRATE_9600
#else
    NRF_UARTE_BAUDRATE_115200
#endif
  };

  APP_UART_FIFO_INIT(&comm_params,
      UART_RX_BUF_SIZE,
      UART_TX_BUF_SIZE,
      uart_error_handle,
      APP_IRQ_PRIORITY_LOWEST,
      err_code);

  APP_ERROR_CHECK(err_code);
};

if I comment this in code "6, 8, APP_UART_FLOW_CONTROL_DISABLED, false," then the ble starts normal but does not send the data to uart.

[PKSHER]

Actually I am having the same issue as 

https://devzone.nordicsemi.com/f/nordic-q-a/13212/nrf51822---uart-init-error

But it is not mentioned there, how to resolve it.

[Dmitry]

You're trying to solve your issue with black magic, usually it's not a good way. First, bring up a BLE part of your system, then connect other parts. In any case, design of your firmware should ensure that wrong data on UART lines won't lock your system down (with or without flow control, no matter).

PKSHER said:

if I comment this in code "6, 8, APP_UART_FLOW_CONTROL_DISABLED, false,"

then you get a broken UART configuration, which may have some nice side effects like normal BLE startup, but obviously not a cause.

Again, without a full schematic of your system (or at least a good photo), it's hard to say anything more..

[PKSHER]

Hello dmitry, yes it was indeed a problem of flow control. When I disable flow control, my ble starts but do not send the data. Then in app_error_check, I removed all the code and just kept the function empty and now it is working as expected. So maybe some kind of error was stopping dongle to work properly. I could not figured out the exact problem but that solved my issue. Now I am able to use transistor with GPIO to switch the other chip I want. Also, the data is being sent out by the dongle.