Help with circuit design for two devices

Thread Starter

danawcook

Joined May 12, 2020
22
I have a variable power supply up to 30V if that is of any assistance while I work on this circuit. Assume I know nothing (apologies) which is unfortunately closer to the truth.

I pulled the amplifier module, 12V - 2A (per power supply), from a Dayton Audio amplifier. My intention is to build a bluetooth mono speaker. I have built my own speakers, etc but have scant experience designing powered circuits.

I have a bluetooth module, 5V - 2A.

I put together a voltage reducing circuit in an attempt to power both devices with a single 12V - 2A DC power supply. Since I did not take into account power, I smoked some resistors and it is unclear whether or not the BT module is functioning. Luckily, I bought spares!

I thought about and read some more about power. Increased resistance in the circuit. Circuit doesn't work now. Not sure where to start/stop.

So, clearly, I need guidance/help with designing this circuit.

Thanks in advance for any/all assistance.
 

MisterBill2

Joined Jan 23, 2018
6,070
You certainly will need a voltage regulator arrangement of some kind to allow a 5 volt device to be powered by a 12 volt supply. For the small amount of power that the bluetooth receiver would be using a linear regulator device will be OK, since maximum efficiency is not mandatory. Exactly what a Dayton Audio Amplifier is, I don't know. So if you provide a description then probably lots of folks can offer advice, which some of it will be useful and some not related at all.
 

dl324

Joined Mar 30, 2015
10,745
You have a 30V adjustable supply and you want to provide 12V@2A and 5V@2A. What is the current rating of the power supply? Is it at least 4 amps?

The 5V circuit is going to require it's own voltage regulator. If it's really going to draw 2A, you should make that a switching regulator.

Are you certain that both circuits will draw 2A each?
 

Thread Starter

danawcook

Joined May 12, 2020
22
The Dayton Audio Amp. I pulled the board from within.

The board inside the Dayton Audio Amp and spec sheet.

The BT board.

Thanks again for assistance ahead of time.

dendad - will educate more per links provided. Yup, the 5V2A was a maximum per description (The maximum operating current is 5V2A. It is recommended to use a regulated 5V2A power supply for better sound quality.)
 

MisterBill2

Joined Jan 23, 2018
6,070
The Dayton Audio Amp. I pulled the board from within.

The board inside the Dayton Audio Amp and spec sheet.

The BT board.

Thanks again for assistance ahead of time.

dendad - will educate more per links provided. Yup, the 5V2A was a maximum per description (The maximum operating current is 5V2A. It is recommended to use a regulated 5V2A power supply for better sound quality.)
I read the power supply recommendation as 12 volts 2A, not 5 volts. That was the supply spec. Not one single word about the amplifier power requirement, ony about the recommend power supply. And I doubt that the 12 volt supply that is listed is regulated.
The BT description is rather confusing because it seems to be describing a device that includes two amplifiers. And it has three different supply voltages listed. It also mentions a REGULATED 5 volt 2 amp supply. I would not deal with a seller that has such a confusing listing.
My suggestion is to locate a surplus dual voltage supply that provides regulated 12 volts and regulated 5 volts. One good and cheap source is resale shops that have an assorted electronics section. But that is what I have found here in Michigan, USA. I have no clue as to where the TS is located.
 

Thread Starter

danawcook

Joined May 12, 2020
22
Seems as if this is my next route.

1590755093219.png

Years ago I purchased a beginner kit with a slew of parts and there is one bridge rectifier with the following text: 2w005G AND five linear regulators of which one is a 7805 which is what I believe I need.

The question I now have is where does the AC adapter end in this diagram. I suspect it "is" the blue box here:

1590755192692.png

But am not-so-secretly hoping that it is contained in this blue box:

1590755247310.png

in order to avoid dealing with the bridge rectifier. Obviously if the latter, I would insert the amp board's power out before C_1 but if the former, I am completely guessing that it is inserted before the rectifier between the plus and minus pins or between the plus and ground pin (left in the diagram).

Thanks again for your attention and help.
 

Thread Starter

danawcook

Joined May 12, 2020
22
It appears that I do not have the capacitors on hand. What a slog to understand different coding but fairly certain I am looking for 220000 picofarad (224 coded) and 100000 picofarad (104 coded) caps. The highest capacitance ceramic i have are 223, 334 which means the 223 is shy an order of magnitude and the 334 is .11 MFD to high.

I am mostly writing this for validation purposes I suppose.

Thanks again.
 

dl324

Joined Mar 30, 2015
10,745
It appears that I do not have the capacitors on hand. What a slog to understand different coding but fairly certain I am looking for 220000 picofarad (224 coded) and 100000 picofarad (104 coded) caps. The highest capacitance ceramic i have are 223, 334 which means the 223 is shy an order of magnitude and the 334 is .11 MFD to high.
You're talking about the filter cap. 0.22uF is too small; you'll have a lot of ripple. I'd use a few hundred uF.

A linear regulator will be inefficient. You're going to dissipate more power in the regulator than in the maximum load. Why don't you just use a USB charger. They make some for Raspberry Pi that will source 4 amps or more; though that's more current than USB cables were designed to carry.
 

Tonyr1084

Joined Sep 24, 2015
4,535
Jumping in here even though you're already getting some pretty good advice: I get the impression you're assuming that a 12V 2A power supply will force the board to use 2 amps. It won't. It just means that 2 amps is the rated capacity the 12 volt supply can produce. The amount of current a device will draw determines the amount of amperage needed.

Let me get extremely stupid for a second: Suppose you have a power supply that is rated at 12 volts and 1,000 amps. Suppose you connect it to a small 12 volt automotive light bulb. That bulb is not going to draw 1,000 amps. The bulb is rated at 12 volts (actually probably more like 14 volts - but never mind that). That bulb is probably a 35 watt bulb. So at 35 watts on 12 volts, that's 2.92 amps. 35 ÷ 12 = 2.91666••• amps. Even though the supply can deliver a thousand amps - the circuit will only draw the amps according to the voltage and the load. That load would be (assuming perfection) 12V ÷ 3A = 4Ω. You would need a supply capable of delivering 3 amps. But if the bulb (the load) was 2Ω then you'd draw (12V ÷ 2Ω =) 6A. If you had a supply capable of delivering ONLY 3 amps then the voltage would drop off to 6 volts. That's why a supply has a voltage and an amperage rating. So you know what the capabilities are. That doesn't mean your project is going to use all the amperage the supply can give. 12V @ 2A and 5V @ 2A, I'm assuming is the rating the supply can deliver. If your circuit draws more than the amperage the supply is rated for then the voltage will fall off. Meaning your circuit won't work.

You also mentioned burning up resistors. Resistors are rated in watts as well as ohms. A 10Ω 1W resistor can handle 1 watt of power flowing through it. Wattage is calculated by multiplying the voltage times the amperage. So if your circuit truly draws 2 amps at 12 volts then that would be 24 watts. IF (and I'm sure this is not the case) you're pushing 24 watts through a quarter watt resistor - yeah, it's going to go up in smoke. When calculating the resistance for a project one has to remember to calculate the wattages as well. Otherwise smoke and fire are forecast for tonights project.
 

Thread Starter

danawcook

Joined May 12, 2020
22
Tonyr - yup. sorted out the power thing but thank you for a cogent explanation as well as the characteristics of the AC adapter. I was aware that it was a max but had no other information since I do not know the load's resistance characteristics and thus cannot calculate the power across the devices. For me, this all goes back to poor grades in EE during undergrad 35 years ago!

dl324 -

label:
1590785296066.jpeg
But I think the issue is moot for two reasons, one being I have many varied and can adjust if need be. This is the one that came with the amplifier.
 

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Thread Starter

danawcook

Joined May 12, 2020
22
Still attempting to verify that this is where I put the devices into my circuit. This comes from after reading the AAC article on Linear Power Supplies. Can I assume that the power supplies (many) that i have contain a circuit generally of this form with rectifier and filter?

1590832948108.png

And thus, my current question is this leads me to want to locate my devices in my circuit with the amplifier at the pink points and the bt module at the blue points.

location of devices.png

Thanks again!
 

MisterBill2

Joined Jan 23, 2018
6,070
As I examine the photo of that power module, it is clear that it is a switching mode power supply, and therefore it is regulated, at least a lot more than those with just a transformer and rectifier and some filter capacitor.
And after I went back to that link to the bluetooth module, I see that it includes amplifiers. THAT is why it is listed as needing a 2 amp power module. This is verified by the two sets of speaker connections shown in the pictures of the PC board. So my very next suggestion, presuming that you have that module and that it is working, is to connect two speakers to it along with the recommended power, which I think is 5 volts, and see if it plays.
BUT it is very important to not connect any of the speaker connections to any other of the speaker connections because the amplifiers are set up for bridging mode operation.
You should be able to do a search for those two amplifier ICs on the bluetooth board and discover both their output power and their working voltage. It might be that you will not require that Dayton amplifier for your music speaker.
 

Thread Starter

danawcook

Joined May 12, 2020
22
I did not consider it important based on questions that I asked but I am building the circuit in order to sum the output of the BT module for mono output. The mono output will feed a single 3-way speaker. so, yes, I need the second amplifier. I will look more closely and test the BT module.
 

MisterBill2

Joined Jan 23, 2018
6,070
I did not consider it important based on questions that I asked but I am building the circuit in order to sum the output of the BT module for mono output. The mono output will feed a single 3-way speaker. so, yes, I need the second amplifier. I will look more closely and test the BT module.
OK, probably you will be able to sum them very simply by using a 1000 ohm resistor from each "+" output terminal to the Dayton amplifier input terminal. I did not see anything about a volume control anywhere, but certainly you will want one. At least, I would want a volume control.
 

Thread Starter

danawcook

Joined May 12, 2020
22
the volume control is on the Dayton amp which will have a single channel running to the crossover network.

Should have also include that the volume pot also has an integrated switch.
 

Thread Starter

danawcook

Joined May 12, 2020
22
5W prob not enough power for 10 inch woofer 3-way design I have but will investigate. I was inattentive regarding BT modules as I was attempting to purchase one without amplifier in order to sum the line outputs. will search for new board as well.
 
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