This module has two GND and VCC pins:

However, this module and this module only have one of each. Why is that?

EDIT: I know most MCU's have a lot of 3V3, 5V and GND pins. This is required for connecting the most varied peripherals simultaneously without exceeding max current output. But I have never seen a peripheral with this configuration. Since I never saw a MCU with only one GND and one VCC pin, and there is a lot of nrf24l01 modules with just one pin of each, I would like to know the purpose, since it's supposed that this module should be connected with only one MCU at a time.

  • \$\begingroup\$ Why do some cars have 2 doors, and others 4? It's a decision that the designers made. \$\endgroup\$ – Matt Young Jun 13 '15 at 23:31
  • \$\begingroup\$ I don't get it. The reason behind rising the number of doors in a car is the same reason in putting 2 pins for the same function? While back doors are used to acess back seats and front doors to front seats, different GND pins are used to access the same ground. Finally, if it's just a designer decision, let them answer me, because they should have something more useful than your answer. \$\endgroup\$ – GabrielRado Jun 13 '15 at 23:43
  • \$\begingroup\$ MCUs rarely have multiple power/ground pins for current-handling reasons, they have multiple power/ground pins for lower power supply impedance. \$\endgroup\$ – Connor Wolf Jun 14 '15 at 1:10
  • \$\begingroup\$ Anyways, the reason is probably that the person who designed that PCB could get 2*5 headers cheaper then 2*4 headers that particular week in Shenzhen. There may not have been a proper reason. \$\endgroup\$ – Connor Wolf Jun 14 '15 at 1:11

There are several reasons why a design can design the use of multiple pins. In order of importance:

  • Connecting two pins in parallel lowers the resistance of the pin connection - a designer might consider low impedance important to avoid interference on the power supply lines

  • There is a limit to the current allowable through a single pin.

  • If power is extremely critical, a designer might decide to parallel two pins to lower the probability of contact problems (improve reliability).

  • Finally, if the host board has already 2 pins wired to each Vcc and Gnd, why not use them?

Note that the single pin board is for soldering. There you take the responsability. If you use a wired connection, you won't have problems.

And your remark on CPUs having many pins for each, is not correct. In CPUs the multiple pins are really to lower the resistance to the power supply. If they'd use only one pin, the socket would probably burn, because of the heat generated in the contact. Also, with a CPU, the power filtering capacitor is on the board, so it is vital that the impedance from the chip to the capacitors is very low.

  • \$\begingroup\$ So should I connect each nrf24l01 VCC pin at a different MCU 3V3 supply pin to rise the current capacity? What about the GND pins? \$\endgroup\$ – GabrielRado Jun 14 '15 at 0:30
  • \$\begingroup\$ Not necessarily - I don't have the datasheet of the nrf24l01, but I can't imagine the current will be that high. Just plan on nice wide traces on the board that will receive the module - and a couple of decoupling caps near the connector won't hurt either. \$\endgroup\$ – jcoppens Jun 14 '15 at 5:25

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