Adding/Extending buttons on PCB

[korcraft]

Hello all,

I'm building a bluetooth speaker. I purchased a TDA7492p board. This has a Bluetooth chip and 50W per channel amplifier.

It also has 6 buttons soldered directly on the PCB.
Play, Back, Next, Volume UP, Volume Down and Power.

I will be housing this board in the speaker enclosure and will not have access to the buttons once inside. My goal was to get some momentary push buttons (2 terminals) and simply solder some wire to the PCB on the buttons and up to these buttons which I could mount on the speaker enclosure.

Now after taking a look though, it seems like the buttons on the PCB have 4 leads not just 2. I'm not sure why they would, but I'm looking for some advice as to determining which leads I should connect these push buttons to.

I don't know if anyone has any experience with these boards or could provide any insight.

Thanks

 

[rayma]

it seems like the buttons on the PCB have 4 leads not just 2.

The switch is likely similar to this one. https://www.sparkfun.com/datasheets/Components/Buttons/SMD-Button.pdf
It's a momentary normally-open (NO) SPST type. Each contact of the switch is connected to two
of the legs. Look carefully to see which pairs of switch legs are connected together on the board.
The good news is that hooking up the off-board switches wrong won't hurt anything (or do anything).

 

[korcraft]

Thanks! This makes way more sense to me. so basically 2 pins are acting as 1 pin.

So I can basically wire up a 2 pin momentary switch to one side of each pair and it should work just fine.

Thanks that really clarified what might be happening there.

 

[rayma]

So I can basically wire up a 2 pin momentary switch to one side of each pair and it should work just fine.

Yes, just pick the "right" side. Try one switch first, and if it works, all of them are likely
connected in a similar manner.

 

[korcraft]

yeh fortunately there are really only two options. Either 2 left and 2 right, or 2 top and 2 bottom...I doubt the button would have diagonal pins connected in pairs haha.

 

[rayma]

yeh fortunately there are really only two options. Either 2 left and 2 right, or 2 top and 2 bottom...
I doubt the button would have diagonal pins connected in pairs haha.

Right, solder two wires anywhere. If it doesn't work, just move one of the wires and it will work then.

 

[Enzo]

You can wire a remote switch to just two of the terminals, but make sure rest of the circuit is not relying on the two pins that are connected together for completing a cirtcuit to something further along. Am I making sense to you?

 

[korcraft]

Yes I understand. Basically this is a play button and a next track button and a volume button. I would be surprised to find that these pins would be doing anything else...but who knows lol.

 

[rayma]

make sure rest of the circuit is not relying on the two pins that are connected together
for completing a cirtcuit to something further along.

These are almost certainly all momentary types.

 

[Enzo]

I still fear I am not reaching everyone. On one side of a switch, the two pins are connected together inside - like a wire. On some boards, rather than running a continuous copper trace to a row of switches, they run a trace to one corner, and continue the trace from the other corner to the next switch, relying on the internal connection to be part of the trace. If we remove the switch from the board, that breaks the through connecction unless we add wire jumpers.

I see it both ways, so just something to be aware of, a simple board inspection wil tell the tale.

Was not implying non-momentary, nor impying a make and break contact. Switches are simple momentary SPST

 

[rayma]

I still fear I am not reaching everyone. On one side of a switch, the two pins are connected together inside - like a wire. On some boards, rather than running a continuous copper trace to a row of switches, they run a trace to one corner, and continue the trace from the other corner to the next switch, relying on the internal connection to be part of the trace. If we remove the switch from the board, that breaks the through connecction unless we add wire jumpers.

Yes, he was going to leave switches in place and parallel an off-board switch with each one.

 

[korcraft]

I understand exactly what you mean.

I won't be removing the buttons thought. I'm leaving them in place and simply soldering a wire to the pins on the button up to an additional button that I can mount on the outside of the enclosure. The integrity of the circuit stays exactly the same but not it has two buttons that with close the circuit momentarily. Pressing either will close the circuit.

And I wanted to add I took at my multimeter last night and grabbed the board and the buttons are in fact as shown above...the top left and top right pins are always connected and the bottom left and bottom right pins are always connected. Pressing the button down connects the two pairs while holding the button down and disconnects the two pairs once you release the button.

So I thank you all for the help and warnings...truly appreciate it. It appears I can now continue with my plan (when the buttons I order arrive).

Also, if anyone has any suggestions for a similar board that's just an amplifier no Bluetooth, that has a great noise floor and sound quality I would be interested in your thoughts

 

[ravels]

Yes, leaving the switches in place and extending wires to panel-mounted push button switches is a good idea. Trying to remove the switches without proper equipment/technique could cause damage to the board.

BTW, those TDA7492P boards are not 2x50W, not sure where those specs are coming from. ST data sheet for TDA7492P states the maximum output power as 2x25W into 8-ohms (and that with 10% THD) The overcurrent protection trips at 4A, so you're not going to get a lot more power even with lower impedance speakers.

Having said that, a well designed TDA7492P amp can deliver close to 2x20W at 1% THD with 19V supply, which is a lot of power for most bluetooth speaker applications.

 

[korcraft]

Yes. I wouldn't have an issue removing the buttons, there's just simply no need to. It would just be extra work for the same results

I have seen these boards being sold at a few output watts...2x25 2x30 and 2x50. I purchased one being sold as 2x50. Any data sheet or pictures posted earlier in the thread were not directly from my purchase, simply all I could find to link for people to see the types of buttons. Either way, I highly doubt I would make use of anywhere near 50W a side.