I want to use a 3.3v microcontroller to share power to control a relay, but the microcontroller stops working after grounding.

xiaoxiaoai88

I want to use a 3.3v microcontroller to share power to control a relay, but the microcontroller stops working after grounding. [Copy link]

 

I want to use a 3.3v microcontroller to share power to control a relay. I use a 5v boost module bought from Taobao. The microcontroller controls the relay using an NPN transistor to amplify the current. Why does the microcontroller not work after the circuit is grounded? How do I modify this circuit diagram? ?

dcexpert

Is the boost module powerful enough to drive the relay?

chunyang

First, measure the change of power supply voltage after the relay is closed. If 3.3V is normal and only the MCU stops running, it means that it is caused by interference. Otherwise, it is caused by insufficient power supply. Obviously, the two countermeasures are different.

chunyang

The simplest test method is to not connect the relay contacts to any other circuits, and only measure the impact of the relay itself on the MCU before and after the action. If there is no impact at this time, it means that it is not a contact spark interference, but a power supply problem. At this time, further testing and analysis is required to determine whether it is a 3.3V power supply problem or a boost power supply problem.

chunyang

In addition, the relay should not be connected in parallel with a resistor, but a freewheeling diode should be connected in anti-parallel.

waterssj

What is that thing in the middle of the relay? It doesn't look like a relay.

xiaoxiaoai88

The relay has a pin, a positive, a negative, and an input control pin.

xiaoxiaoai88

waterssj posted on 2022-7-29 15:39 What is this thing in the middle and bottom of the relay? It doesn't look like a relay.

That is ground. The relay has 3 pins, one positive, one negative, and one input control pin.

xiaoxiaoai88

dcexpert posted on 2022-7-29 14:55 Is the power of the boost module large enough to drive the relay?

The power is sufficient, but the main problem is that the microcontroller is not running.

bigbat

Can you draw the schematic diagram first? This diagram is really hard to understand. The relay coil has only two wires. The control pins should not be related to the MCU motherboard. The execution components should not use the same power supply as the MCU power supply.

xiaoxiaoai88

bigbat posted on 2022-7-29 16:32 Can you draw the schematic diagram better first? This diagram is really hard to understand, and the relay coil has only two wires, and the control pins should not be connected to the MCU motherboard...

I just want to use the same power supply. I don't want to power it separately with a dry battery. IN is the control pin of the collector.

xiaoxiaoai88

xiaoxiaoai88 posted on 2022-7-29 16:43 I just want to use the same power supply. I don’t want to use a separate power supply for the dry battery I use. IN is the control pin of the collector

in is the control pin of the relay, and the io port of the microcontroller is connected to the in pin through a transistor

bigbat

xiaoxiaoai88 posted on 2022-7-29 16:44 in is the control pin of the relay, and the io port of the microcontroller is connected to the in pin through a transistor

I tell you to draw the circuit diagram correctly, otherwise no one will know how you connected the wires.

Can you understand this picture?

fxyc87

This kid posts everywhere, and the entire internet is filled with just this one post of yours.

秦天qintian0303

You can debug the program online to see if there is any hardware error, and then use an oscilloscope to see if the power supply drops at the moment of power-on. Generally, a voltage drop in the microcontroller at an instant will cause a reset, resulting in an abnormality.

suncat

Looking at your circuit diagram (which is also not standard), the relay has three terminals used. One of them is directly grounded. I don't know which one is the common terminal. This solution may cause a short circuit. You'd better fully understand how to use the relay terminals.

eli002

There is something wrong with your relay circuit diagram. The transistor is always in the on state. At the moment of power-on, 5V passes through the coil and there is a possibility of direct short circuit.

Honghuzaitian

Is the current enough? The transistor has a current limit, right?

海兴晶锐

To achieve signal isolation and power isolation, the relay has such a large working current that it is very likely to lower the working voltage of the microcontroller.

dabiaoke

You can use the elimination method. If the microcontroller is normal after disconnecting the relay, then check the power supply problem. Is the 3.3V pulled down, or is the interference too strong to affect the reset?