nrf uart data transmition /receving gps/gsm data

[jd3841]

hi
i am trying to communicate with two devices throught UART , in nrf51 device uart i get a voltage of 2.83 v with .0238 milli ampere while in gsm module uart pin i have 4.0 V so will it be give any issue while making a communication , will it shortcircuiting my device if i am connecting with each other

[Daniel Wang]

Yes, you cannot do that. 4V is too much. Absolute max is VDD + 0.3 V

If you have VDD= 2.83 , max is 3.13 V

[jd3841]

so how will i connect with each other to make communication for data transmition

[mtsunstrum]

You can add a level-shifter IC ... or a cost-effective way is to install a series resistor between the UART signals (e.g. 20K)

The value of the resistor may need to change depending on the UART baud rate you are trying to achieve.

[mtsunstrum]

But be careful in the other direction ... from nRF51 to GSM UART ... the resistor method cannot work in that direction. Most likely solution is a voltage level-shifter IC.

[jd3841]

thanks but will u please explain me in more details by taking any example

as on before of now i am trying to make a connection from ardino uno board with gsm+gps module in which it work but with nrf51 i did't try

ardino uno reading is 5.0 V, 70 milliampere

while nrf reading is 2.83 , 0.0238 milli ampere

gsm uart reading is 4.02 V 15 milli ampere

SO SHOULD I MAKE DIRECT INTERFACE OR NEED TO USE LEVEL SHIFTER IC

[MartinBL]

Hi,

As mtsunstrum said, you cannot connect 4 or 5 V signals directly to the nRF51. 

You might be able to connect the nRF51's UART TX pin directly to your GSMs RX pin, but it is not certain that it will work. You cannot however, connect the nRF51's RX pin to the the GSM's TX pin. Then you risk burning up your nRF51. So yes, you will most likely need some sort of voltage level shifter. You can read more about it here. 

[jd3841]

I HAVE FOUND THIS FROM MY DATA SHEET SO SHOULD I USE A  LEVEL SHIFTER OR NOT

[MartinBL]

Yes, you should use a level shifter. 

[jd3841]

thank you martinBL