Trying to mod Sony HWS-BTA2W for auto-power on

[theSovereign]

Howdy folks, I hope this is the right forum for my post, and hopefully someone can help me figure this out -- if it is at all possible.

I've done some console modding in the past, installed carPCs in a couple of cars, done a bit of soldering here and there, and I have alot of interest in electronics, but unfortunately I'm pretty clueless when it comes down to the nitty gritty of electronics.

Ok, so finally, here is the reason for my post:

I have a **broken link removed**, which serves either as a Bluetooth transmitter or receiver. I will be using it as a receiver in the car, plugged into the aux-in of my headunit so I can play audio from my phone wirelessly via A2DP.

The HWS-BTA2W will be connected to a switched auxiliary power outlet in the car, so it will be turned on when the engine is running, and off when the engine is off. Unfortunately the HWS-BTA2W does not automatically turn on when the unit receives power, and requires the power button to be pressed.

The power button functions as follows: If the unit is off, press briefly to turn it on. If the unit is on, if pressed briefly it does nothing, but if held down a little longer, it turns the unit off.

What I'd like to do is mod it so that it automatically turns on when it is receiving power, this way it'll save me a step when I get in the car, and I can also "bury" the unit in the dash.

Unfortunately I don't have a schematic for it, but I did take some fairly decent photos of the front and back of the PCB, which I hope might be helpful. I can provide higher resolution photos / PSD if needed.

The key to the numbering is as follows:

1 - Power button
2 - Pairing button
3 - Transmit / receive mode selector switch
4 - Power input
5 - Line out
6 - Line in

I forgot to label the LEDs, but the top one is the Power indicator LED, the bottom one is the Bluetooth connectivity inducator.



In any case I hope this isn't an impossible feat and thanks for your time!

 

[theSovereign]

Hmmmm... no takers... is attempting to circumvent the switch circuit not feasible?

Would I just be better off just using a constant-to-momentary relay type circuit to activate the power switch, something like this: **broken link removed**

 

[theSovereign]

While I'm at it, here's another question:

The HWS-BTA2W's power requirements are 4.5V, 500mA -- in order to power this from the car's accessory outlet without having to shell out $30 at Radio Shack for an adapter, would I be able to step down the 12V simply by using a 40Ω resistor inline with the +12V line? Or is stepping down the voltage more complex than that?

Thanks again...

 

[MikeMl]

There is more to dropping the voltage than just a resistor. You will need to use an LM317, two resistors, two capacitors, and the LM317 (TO220 package) will need to be mounted on a large slab of metal (the car).

For the PushButton, you will need to do the following test: Power the device on 4.5V. Figure out which part of the device is connected to 0V (not +4.5V) out of the power supply. Hopefully, that will be the "chassis" (ground). That is the part that will eventually be connected to the vehicle ground.

Then take a DMM, and measure the voltage from EACH end of the On/Off switch to the chassis ground. Record both voltages. Then record the two voltages again with the button pushed. One will likely not be effected by pushing the button; the other will. To design a "button pusher" circuit, I would need to know those two voltages...

 

[theSovereign]

Thanks for the reply.

Regarding the pushbutton: if my understanding is correct, first I need to figure out which of the legs on the power input (#4 in the photo) is the ground, and then use a multimeter to measure the voltage on each of the legs on the power switch (#1 in the photo), recording the voltages for each leg, both while powered on, as well as powered off...?

 

[MikeMl]

Initially powered off. Then while the button is being pushed, presumably the button either grounds something, or feeds power to something. That is what I'm trying to figure out?

 

[theSovereign]

Ok, so here's what I've got:

I used the multimeter to take readings from the ground leg (outside of the barrel connector, since it has a positive tip) to each of the three legs of the power switch: the readings were virtually the same both when powered off, and on:

Off: each outside leg measured 1.802V and the center measured 0.000
On: each outside leg measured 1.800V and the center measured 0.000

Is that at all helpful?

 

[MikeMl]

Ok, but what happens to the voltages WHILE the BUTTON is PUSHED????

New test: with unit OFF, put your DMM in OHMS mode, and measure the resistance between the two pins on the switch that have the same voltage on them. I think you will see a short.

Measure the resistance from the switch pins to ground, too.

 

[theSovereign]

Aaah, while pressing the power button.

Sorry, my reading comprehension skills are usually much better. Will report back.

 

[ZR1000A1]

Hello,

I understand, that this thread is rather old, but did you ever make it work (I mean PushButton mod)? I'm going to buy this device and wonder if it's doable at all.

Thanks

 

[Nigel Goodwin]

Hello,

I understand, that this thread is rather old, but did you ever make it work (I mean PushButton mod)? I'm going to buy this device and wonder if it's doable at all.

Thanks

Many years ago I did this for old cam-corders, using two 555's - one as a power-on delay (to give the circuit time to settle down), and the second to give a brief pulse to short out the switch contacts via a relay.

It was done to use old cam-corders (with duff heads) as security cameras.

 

[ZR1000A1]

That's exactly what I'm looking for! Do you still have the schematic diagram by any chance?
Thank you!

 

[Nigel Goodwin]

That's exactly what I'm looking for! Do you still have the schematic diagram by any chance?
Thank you!

No, I never drew a schematic, and it was even pre-internet

But it's just one 555 as a power up timer, feeding another monostable to give a timed pulse.

If it had been in the last 15+ years I've have used a PIC to do it.