Hello all.
As my first proper SMD project, I have made myself a multi-purpose board for my prop building.
Has literally everything I might need on board. I won't bore you with the details.
AMAZINGLY.... It all works and quite well. Not for sale or anything, just for me.
There is a PAM 8406 amplifier on board, which is working well (no real hum or interference which I find amazing for a first board).
I basically used their example circuit in the datasheet. But, I still get a 'pop' when it switches on.
Not terrible, but getting rid of it would be nice.
The tech spec for the amp says it has anti-pop, but my speakers do pop a little.
Any ideas how to mitigate that? The power to the amp is controlled through an N-channel mosfet (so I can isolate it when not used).
There is also a mute function which is also available to the processor if I wish.
I have yet to sit an draw the madly complicated circuit diagram, so I can't provide that yet.
Work on the basis that it is the circuit in the PDF.
The only thing I can 'hear' through the speakers is the HC-06 Bluetooth module when that is plugged in. They are very noisy. Even then however, it's barely noticeable on full volume.
I don't see the point of turning off the power to the amplifier, just use the mute input.
If you are controlling the power with an N channel MOSFET that suggests you are disconnecting the 0V connection, doing that will lead to complications you could do without. For example, if the supply is still connected you have possible phantom connections to ground through other pins and even possibly the speaker, you have to be very careful with these. Simplest is not to disconnect the power but use the mute input instead.
Thanks. Yes, next version I will bin the power switch and just use the Mute facility.
Came out FAR better than I thought!
Onboard 3W stereo Amp with pre-amp outputs and onboard volume
Connector for JQ8400 MP3 module over serial (my default MP3 module). Has onboard flash and USB abilities.
Bright Heartbeat LED (I always have one of these - easy identification the loop is running)
Self reset ability. You can trigger the reset pin low from code.
Onboard SD card
Onboard IR receiver
Onboard IR transmitter
External IR out
External IR in
4x PWM outputs
8x Standard 0-5v inputs (through a MCP23017 multiplexer, so you can change them to outputs)
8x Optically isolated inputs
8x Standard 0-3.3v outputs (through a MCP23017 multiplexer, so you can change them to inputs)
8x Mosfet switched outputs
8x Analogue inputs
1x External serial port
1x External I2C port
800mA 3.3v bus
5A 5v Bus
9v-40v DC input with reverse protection
Onboard 4 pin serial connector for a HC-06 Bluetooth module - I can then also use an nRF24L01 instead.
Onboard 4 pin I2C connector for a 128x64 OLED screen (can be used for anything I2C)
Onboard 4 pin I2C connector for a 128x32 OLED screen (can be used for anything I2C)
Onboard Piezo
Onboard DS3231 Real time clock with battery backup
Dedicated DS3231 reset from code
2x I2C positions for 24LC#### EEPROM chips (if I can ever find any in stock)
Onboard dedicated dip switch
This board is full populated, and that is not likely to ever be the case. But, I needed to test everything.
I wrote a test routine for all of its functions and all seems well. Had a slight issue with the opto-isolator resistor value (4R7 in the 4K7 bag ).... but got past that.
Next version?
Will delete the switch to the amplifier.
Add a LED to show mute is active
Move the optional 10k hold-down resistors on the inputs to a slightly better position for soldering (maybe underneath)
Maybe put an 'onboard' Bluetooth module on it.
I think I have it solid wired high (I know it has a pull-up). I might use the now spare mosfet that used to switch the power to the whole amp to operate this shutdown feature
Understood.
FYI, the professional preferred method depends
on whether a suitable solder station is available. We use this one at work. If it is available then 0402
SMC 0-Ohm resistors are used to connect pullup or pull down resistors. If it isn't then a regular
value resistor is used and solder pads are provided to solder bridge the resistor to either +V
or GND. (the pad connected to the resistor in the middle and the GND and +V pad on either
side so all you need is an ordinary Weller iron and solder to bridge it to one side or another.
Back in the day all configurations were set with DIP switches but that has mostly fallen out of
favor although it is still a viable solution. If I had your board in my lab I would just cut the trace
that pulls it high and add rework 30 guage wire wrap wire to connect it to a processor GPIO
so it can be S/W controlled.
I just redesigned the board for a second version. I knew there would be adjustments to be made and I am very happy how it's worked out so far.
0402! At 53, it's a challenge for me to work with the 0805's!
I have indeed now used the Mosfet that was in place to switch the power to the amp to instead operate the Shutdown feature. So I have Shutdown and Mute available hardwired. Probably overkill, but they were in place, so might as well use them.
Added a couple of Leds to indicate mute and shutdown state as well.
As for the wire-to-board connectors, they were too small. Where I opened a couple up very slightly with a drill, it was enough to give me slight issues with the through-board connection at that point.
Live 'n' learn and all that.
Biggest issue? PARTS! Digikey, RS, Mouser, Farnell..... nobody has anything. Nobody has the MOCD208 Opto-isolators until October this year apparently.
So, love or hate China (let's not go down that route), I had to resort to AliExpress. OK, it's a couple of weeks wait, but 10x MOCD208 isolators were $3.80 delivered.
Highly likely to be knock-off's or rejexts, but at least I can progress. Saying that, this board is probably populated with 70% AliExpress just due to no availability anywhere else.
Yes obvious, but being in the land of kinda unemployed (Lost job during Covid), I am being careful with my pennies at the moment.
I designed and 3d printed a stand for my phone and UNBELIEVABLY the free microscope app on it works very well.
Pics look a bit blurred but they are crystal clear. Also I can take video or snapshots (if I ever needed to).
See me through until times are better
It's literally impossible to find ANY SMD part in the UK (or the US).
I need some TTSOP MCP23017's..... RS, Farnell, Mouser, Digikey etc, all out of stock of absolutely everything until the end of the year.
Out of 15 different IC'c I need, they only had one of them between them all.
No. Everyone in the UK appears to be out of literally everything. I knew there was a chip shortage, but lead times (that I doubt are accurate) of around a year is madness.
RS and Digikey who I use a lot are particularly bad.
Oh well, long wait for dubious quality Chinese stuff it is
(Nor does mine!)