Identifying Issues in an Electronic Circuit

Hi everyone
I have some questions in my schemetics

HR98 relay is DPDT relay. if 7->6 (320ohm coil) have 12V, 9~8 are connected

I ordered a PCB that includes the aforementioned circuit and proceeded with testing it. According to the PCB design, both pins 12 and 7 are supposed to simultaneously receive 12V. However, during testing, I observed that current is only flowing through D1 (Diode) and the 12-1 connection.

I used a multimeter to measure the voltage at pin 7 and confirmed that it is indeed receiving 12V. However, I found that pin 6 is not receiving any voltage.

so I directly connected pins 7 and 6 outside of the PCB using a wire like the image. Upon doing this, I observed that the relay activated and the H3FA-a-dc12 component began functioning as expected.

can you explain why it happen

Where is the diode D1?
Is this two independent relays in the one package, otherwise why two coils? Can you post a data sheet for the relay?

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I’m guessing the HR98 relay is the one here:

You should not have a dashed line between the two coils, the relays are not mechanically ganged, they are independent. It’s not a DPDT relay but rather 2 SPDT relays.

Why should pin 6 receive any voltage? It’s at ground potential, according to your first diagram.

If you really wired up pin 7 to pin 6 as in the second diagram, you would be shorting out the 12V supply.

Why are you connecting the relay coils to a constant 12V? That would keep them on all the time.

Maybe you really wanted to drive the coils from the NE555 and the H3FA, whatever that is. If you do that, you need a flyback diode to snub the back EMF. Or maybe you are switching something to the NE555 and H3FA. Cannot tell without more context.

From all these errors, I’m sorry to say that I conclude that you don’t know what you are doing. Even though it’s a KiCad schematic, you need advice on designing circuits, which this forum is not for.


Ohhhh :frowning_face:! I wanted to know the relay type. Maybe one coil was measured incorrectly and is “hold” resistance, whereas the other is a lower “make” resistance?

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i don’t have datasheet about that relay, confirm this site

I also thought that a short circuit would occur if pins 6 and 7 were connected as shown by the red line. Therefore, the relay coil between pins 6 and 7 should not be energized, and the relay should not operate. However, currently, when pins 6 and 7 are connected with a wire, the coil activates outside the PCB. Could you explain this situation?

It seems that the relay pins do not match the symbol shown. I doubt the Gnd is connected according to the schematic either.
Sorry, can’t comment any further without a data sheet for the relay and the PCB layout.

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I think you have not correctly numbered the pads. It’s impossible to say without seeing the footprint and comparing it with the diagram in the datasheet.

It’s dangerous to go around with a wire trying different combinations. Better to get the pins and pads correct by reading the datasheet carefully. You should also verify the coil pins by using an ohmmeter. You should be able to tell the difference between the NC contacts which will be 0 Ω and the coils, which should be 330 Ω. The NO contact you have to check after activating the coil. All this can be done on the relay outside of the circuit.

Also remember that the PCB pads are usually numbered looking from the component (usually Front) side, while the relay pins may be looking from the bottom or from the top.

As jmk said, you need to post more information.

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this footprint is what i maked

this is schemetic that company post on their site
this is part of my PCB design in kicad

Not sure why you chose your numbering when the datasheet already provides one: 1 = common contact, 2,3 = coil, 4 = NC, 5 = NO. Since these are independent relays you may wish to make a symbol with 2 units.

As I said, test the relay outside of the circuit board with an ohmmeter, and then a 12V source, once you have verified the coil pins. On the board who knows what you didn’t show is connected to those tracks.

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Not possible.
Only what should be activated by such connection is the fuse in your 12V supply.

On the other hand if you want to have coils permanently connected to 12V then why to use relay at all. Replace relay with connections it makes when coils are connected to 12V.

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I agree with the others: in your original schematic the relays are permanently operated (12V one side, GND the other side of both coils), so there is no point in having the relay at all.

It is also clear that your pin numbering and the pins on the relay package don’t agree, hence all the confusion.

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I apologize for any confusion and appreciate everyone’s willingness to help. The circuit in question is a part of a larger circuit. The 12V power to the coil is designed to be supplied only under specific conditions.

Currently, in my situation, the 12V-pin12-pin1-GND/12V-1k-D1(LED)-GND path is working correctly, with 12V being supplied, the diode lighting up, and the upper part of the relay functioning. However, in the 12V-pin7-pin6-GND path, the relay’s lower part is not activating, possibly because there is no voltage. To test, I connected pin 7 to pin 6 with a wire outside the PCB. I expected a short circuit and that the coil would not operate, but surprisingly, the coil activated and the H3FA-a-dc12 component received power. Simultaneously, D1 (LED) turned off. The voltage was still correctly applied to pin12-pin1. I am grateful for your help in this confusing situation.

It’s time for me to leave the workshop, so I won’t be able to conduct any direct tests at home. I will continue to check for errors in the PCB and the circuit at home, and I will share the results with you tomorrow. Once again, I apologize for the inconvenience.

I think what happened is you did short the 12V supply because your pilot LED turned off, and what really happened is you deactivated the relay. But because you have the NC and NO pads swapped as your footprint is viewed from above, but the relay pin labeling is viewed from below, it caused the circuit to be closed, as desired.

This also happens with tubes whose pins are viewed from below. It’s a trap for people used to working with ICs with pin labelling viewed from above.

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Hi @junbae

As Retiredfeline says:

Looking down at the front of your PCB, the pad numbering should look like this:

Not this, as you have drawn:

To correct your footprint problem, open your footprint in the Footprint Editor, select the whole footprint and Mirror it across the X axis.

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So sometimes there is 12V. The same 12V is fed further through the relay. If relay is configured that way that it fed 12V when its coli is powered than relay is not needed. Just connect 12V to the output and 12V will be there when 12V will be supplied - exactly as with relay.
If relay is configured to not put 12V at output when its coild is powered then relay is also not needed - when 12V is than it is not connected to output and when 12V is not present it is put to output so you never have 12V at output.


I think OP drew a separate circuit rather than showing us the real circuit and gave the same misleading 12V label to what are actually separate wires and also not constant voltages. Poor problem description.

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Thank you to everyone who offered their help. After testing at the workshop, I realized that, as you all mentioned, I didn’t design the footprint correctly. I will be more careful in the future to avoid such mistakes. Thank you so much! :blush:

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It’s not just the footprint. The underlying logic is wrong, too. Read the post from @Piotr - as drawn, you don’t need the relay at all. Don’t just patch up the footprint and carry on; take a breath and rethink what you are trying to achieve.