Well, the out-of-spec (low) voltage is easily solved. As you suggested earlier, just use a higher voltage input to Vin. The 12V from the car itself will work, but will also generate unneeded warmth.

Pretty much any DC-to-DC voltage converter will work -- there are tons of them on eBay for about a buck apiece.

The Arduino Mega schematic has some circuitry around the Vin/USB parts that looks like it is intended to cut out the USB power when powered from Vin. So it _might_ actually be safe as-is. I just found it a bit odd to measure 5V at the (unconnected) USB connector when powered via Vin. And the slight reverse current I measured isn't enough to worry about, so long as it stays that small.

Perhaps I'll try a couple more experiments with it and see if I can uncover evidence one way or the other.

Yeah, I think it is fine. I'm powering the Arduino with +9V via the black power jack (aka. "Vin" plus a diode), and I've added some mechanical relays onto the +5V output to act as a significant load (about 0.22amps total at 5V). All with the Betz board powered from the 3.3V output of the Arduino.

Then.. connected +5V to the USB connector through my voltage/current measuring dongle to look for current flowing there. It reads 0.01amps, which is effectively ZERO here.

So, yeah, with sufficient voltage on Vin, the USB connection appears to be safe. Which kinda makes sense I suppose, given the intended customer base for these things.

EDIT: Note that if you connect to the +5V pin on the Arduino rather than to Vin, it will probably power just fine at 5V. But this also bypasses the USB safety circuit, so I don't advise it for this case.

Eg. This kind of thing: one does have to use a voltmeter for initial setup, measuring the output voltage while turning the tiny potentiometer adjustment to get 7.0V from it.
https://www.ebay.ca/itm/DC-DC-Buck-Step-...le/112472493337

Or these more expensive ones, which have a hardwired output voltage (use 9V in this case):
https://www.ebay.ca/itm/Power-Supply-12V...le/232328740718

Again, I don't see any need for such -- the Arduino board ALREADY HAS A 3.3V LINEAR REGULATOR onboard!

Thanks so much for doing all that work and verification, Mark!

This is fantastic information!

I'm so glad I'm not endangering the computer by powering VIN and plugging in a computer at the same time.

I'm going to think about my various power options now, with that information.

The one I got looks identical in the photos, other than the brand name: https://www.amazon.ca/gp/product/B01BY167MI

The design is pretty darned close to the official version, https://store.arduino.cc/usa/arduino-mega-2560-rev3 but with very slight differences in the layout.

You may want to just simplify things, and run +12V directly to the Arduino's power jack.

This project uses very little current; it is a low power setup. I have it running on the test bench here, and the 12V current draw is only about 160 milli-amps (0.160 amps). Multiply that by the voltage (12V) to calculate wattage, giving about 1.9 watts total. The Arduino's onboard 5V regulator is hovering at about 28C (82F), with room temperature at 22C.

Compare this with inserting an extra, 95% efficient, DC-to-DC converter, to drop the 12V down to 7V, for input to the Arduino's 5V regulator. This would have a 5V drop (12V to 7V), and assuming the same current flow it would save (5V * 0.156amps * 95%-efficiency) about .75watts. So the setup would still be using about 1.2 watts, compared with 1.9watts without it.

The 0.75 watt savings are probably not worth the hassle/expense in this case, given that the circuit draws so little power. An extra 0.75 of a watt in heat is negligible here.

So I would just ditch the DC-to-DC converter altogether, and feed 12V directly to the Arduino, and use 3.3V from the Arduino to power the Betz board.

EDIT: If you were to forgo the USB connection, you could power the Arduino from a 5V DC-to-DC conversion. In this case, the converter would be dropping from 12V to 5V, a 7V differential, saving us (7V * 0.156amps * 95%) a whole watt. So power consumption would drop from 1.9-watts to 1-watt. That might be enough of a saving to consider the extra DC-to-DC conversion, but I still would not bother.

If the circuit used a lot more power, say in the 3-watt+ range, then yeah. But at 1.9W ? WTF cares?

It would be quite useful if you could try powering your rig similarly, with 12V directly to the Arduino, and with an ammeter inline to measure the current draw in the vehicle.

I expect it to be a bit higher than what I get on the test bench here, but not much higher. Still.. real measurements trumph theory in my books!

Thanks so much for that detailed information! That's really super helpful.



I ruled this out even before starting any design. It was my first question when starting research. When I googled about this, my results turned up answers that fell into two camps:

- Amateurs like myself who said "the specs say an Arduino should be able to take 12v so you should be fine".

-People more experienced with Arduinos, warning specifically against connecting an Arduino directly to car voltage, because they know that car voltage varies widely, and can spend long periods of time at 13v or higher, and can spike even higher at times.

The Arduino's voltage regulator lists 12v as its upper limit, and the more credible-sounding search results cautioned against exceeding that. In all cases, they recommended using a separate power supply, which is where I started on my path of trying to find a good one. My initial attempts at using a 7805 regulator with caps and heatsinks was from sites with schematics of how to power an Arduino correctly off of a 12v source.

One saving grace would be if the Empeg somehow already regulated that amp remote wire, the place where the power is coming in to the molex tuner connector we're using. If the Empeg prevents that line from going above actual 12 volts, maybe it would be safe to use it. I made an assumption that, since the Amp Remote wire is 12 volts, that when it was on, it would be just delivering the same car voltage as was coming into the player in the first place. I didn't think it would be going through another voltage regulator.

But now that I think about it, that assumption might be completely incorrect. I seem to recall asking about how much current I can draw off of that wire before, and I vaguely remember being told there were some amperage limits on that wire. That would mean that it does indeed go through some kind of voltage regulator. Do you happen to know if it limits the voltage on that line?

I'll look into this. It would simplify the design and construction quite a bit if I could do this.



Extra heat concerns me of course, since my design is intended to get stuffed into wiring bundles in dasboards and trunks and such. So I'd have to see just how much extra heat really occurs, with a touchy-feely test. Of course, the empeg gets warm in spots too, and seems to do fine most of the time.

Thanks again!

Rather than relying on hearsay from "internet experts", just go and look for yourself firsthand.

The Mega board we have uses an AMS1117 as the 5V regulator.
Here is the datasheet for that regulator:
http://www.advanced-monolithic.com/pdf/ds1117.pdf

Maximum input voltage is shown near the top of page 2. 15V DC.

If you instead use a Genuine Arduino branded Mega board, the specs for that board are available from Arduino here:
https://store.arduino.cc/arduino-mega-2560-rev3

Scroll about midway down, and click on "TECH SPECS".
It will show you Input Voltage (limit) 6-20V.

So all good on that front.
But do read it yourself, rather than accepting as truth what other armchair engineers might claim.

And if you are worried about "spikes" beyond the rating of the regulator, it is pretty simple to just put a zener diode across the input (12V to GND) to provide spike regulation to whatever value you select. Eg. a 14V Zener will limit the spikes to 14V or less.

*raises hand*

Me! Perhaps when you really want to gauge interest, a post in Off Topic or General might catch a few more lurkers.

Cool. What would your preferred form be? I haven't decided how I'll offer it.

A. I send you my blank PCB and a link to print the enclosure on Shapeways, with a bill of materials listing all the necessary parts, and you order and solder the parts yourself? I've designed it so far so that all soldering is all through-hole 0.10" components. I would sell you merely the blank PCB, and everything else you order yourself, but I'd give you links to everything.

B. I send you a populated PCB with all the circuits and connectors soldered in, but you have to buy the Arduino board and the BetzTechnik board yourself, upgrade both of their firmwares, and plug them together. It would still require you to solder some pin headers onto the Betz board, but that's pretty easy. I'd supply the correct pin headers to make sure they mate up with my PCB.

C. Fully assembled, all parts sourced by me.

Ballpark prices below. I don't have solid numbers for everything yet. For any items I'm supplying myself, I'll add a small margin of a few percent to help cover my costs and time. A few bucks more if I'm doing any soldering or assembling.

The board price for my PCB would be my unit cost for the low-production-run PCBs from Pad2Pad, so the individual cost per board is still kinda high, my blank board would probably be in the $40-$50 range plus shipping.

The enclosure from Shapeways would probably be about in the $60-$80 range plus shipping depending on whether you pay extra for a rush production. I don't know the exact price since I haven't finalized an enclosure design yet. That will occur after I print my next PCB revision and test it.

The BetzTechnik boards run about $60.00 plus shipping (including the WT32i chip).

The Arduino Mega boards run about $20.00 plus shipping.

I haven't priced out the circuitry and components for the remainder of the stuff. I was buying components in bulk so I'd have to look them all up. Figure somewhere in the $40-$80 range for all the circuits and connectors? Not certain.

Finally you'd need to be comfortable with doing this to your player, since I'm not really to accept other people's rare unobtanium artifacts into my care:
https://github.com/tfabris/BlueGigaEmpeg/blob/master/I2S%20Wiring%20Modification%20Photo.jpg

I'll do a more detailed post in General when I've got something closer to final and can post a good video demo.

Mark, thanks so much for that additional data about the voltage regulator on the Arduino board.

I tried hooking it up to 12v on the test bench, and the Arduino board got a lot warmer than I'd like it to get for a car installation.

So what I'm trying next is just ordering a different Pololu voltage regulator that is pin-compatible but outputs 6v for the Arduino VIN pin. We'll see how that does.

Sounds good. Except you'll want 6.5V (minimum) output, not 6V. Per the design recommendations in the datasheets linked above.


Which means it guarantees correct operation (of the Arduino board's 5V regulator) under all conditions only when the input voltage is at least 1.3V higher than the desired output voltage. So for a 5V output voltage, it requires 6.3V or higher as input.

It will "happen to work" with lower input voltages at room temperature, with a light load. But as you seem to be concerned with the huge swings in temperature that regularly occur inside a vehicle, one really needs to keep it fully in-spec.

Thanks so much for that, Mark. That is super useful information to me.

I'd probably go with option B. I have a basic Radio Shack soldering iron, and while I'm not afraid to use it, neither do I have a lot of experience beyond soldering wires for installing car stereos, etc. Plus it would leave me with enough to do to have a little fun and learn a bit.

Since I don't have an immediate need, and I'm on a very limited budget, I'd probably just buy your PCB and the BetzTechnik board right away and then wait on the rest until I have an actual use case.

The other thing to consider is that things can be significantly harder or more expensive to get here in Mexico if they can't be found locally.

FWIW: The Arduino mega boards have been used for driving 3D printers for some time. Some versions (Taurino power) can run with up to 24vdc input.

http://reprap.org/wiki/Taurino#Taurino_Power

OK, that's pretty cool. I didn't know about those. Nice. Hm.

Ah good point.

I am working with the Shapeways 3D print of the enclosure and it's coming out way more expensive than I predicted. Base price is $71.00. I'll see if I can get that down some.

I have a friend (Russmeister here on the forums) who works for Markforged. Want me to ping him and see if he can print up a few samples for you?

I had a look at the MarkForged product line and that style looks like way overkill for what I'm trying to make, based on the types of materials they do. Looks super cool though. I'm not sure that my enclosure falls into a category that might be considered in the range of "Free sample", though I won't turn down free stuff if offered! It's in two parts, total of about 600 square centimeters in shape (don't know how much actual solid volume since it's mostly hollow).

In the meantime I've done some trimming of part thicknesses and gotten the Shapeways base price down to about $59.00 which is a bit better but still not great. I'm going to try some more trimming work.

In other news:

My current prototype unit has, after some important software bug fixes recently, run stably and without issues for several days now. The empeg and the prototype have been fully mounted in the trunk and the display board mounting in the cabin is long since done. Everything works: Start the car and it plays perfectly and all the AVRCP track stuff works perfectly. So I'm feeling pretty confident about it overall. I still fully expect that new users of the software will encounter new bugs when they try to pair it up with new gear, but I'll help work through any issues as they arise.

I have a new Pololu power supply waiting at home to try out (even though the 5v one has been running stably for weeks, I still want to make sure everything works to spec at 7.5v). I'll solder it into the prototype and see how it goes.

I’d be interested in 1 (maybe 2) fully assembled modules.

Keep up the good work!

Awesome! That helps me decide how many to order from Peter Betz when he's ready to make new boards. My impression was that he was in-process on ten more, so I'm going to get several from him so I have a buffer.

I've been going through the parts prices and I think I'll be offering the BGE for about this much. This covers basically my costs for obtaining the parts and assembling them, with a very small margin to help cover my time and effort. I'm not trying to make a profit on these since I know there will only ever be a handful made. Just want to make something cool available to the empeg owners that need it.

1. BlueGigaEmpeg PCB and components, assembled: $79.00 plus shipping.
Does not include:
- 3D printed case, I'll give you the Blender file so you can have it printed yourself.
- BetzTechnik Bluetooth board, you'd need to order it yourself, update its firmware, cut a jumper, desolder a capacitor, and solder on the pin headers.
- Arduino Mega board, you'd have to modify the Arduino compiler yourself and upload the BGE firmware.

2. The same as above, but I send you the 3D printed case too, prechecked to guarantee fit: $159.00 plus shipping.

3. Fully assembled box with the Betz Board, Arduino, and BlueGigaEmpeg board inside, with all firmwares preloaded: $259.00 plus shipping.

All of the above still requires that you perform this modification to your empeg interior, so this project is only for folks who can already safely disassemble their player without snapping stuff off the back of the display board (or other kinds of damage) in the process. It also requires updating Hijack and Config.ini on the empeg.

The above is a preliminary non-final estimate. I don't have my first 3D printed prototype of the case yet (it's on its way), and I don't have the final PCB's from Pad2Pad yet (they're on their way), and I still haven't got any additional boards from Peter Betz yet (he's kind of taking his time on them).

Sound OK?

This is one of those situations where the right answer is that I should do nothing(*) but I'm in for #3, and I'll have to figure out how to get set up to solder here.

(* I'm driving a car which is a 17 year old hand me down and which I'm sure will die at some point; It was given to me by my family while I was homeless and my job wasn't paying me, and my hope was that I could make it last through the surgery I had January of last year. Well, I had two more surgeries, last month, and it carried me through those, too. But I'm sure the instant I do anything to improve it, it's gonna die)

You have a 17 year old car with Bluetooth? Wow!

I’ll also take 1 piece #3 when available. Congratulations on a successful project!

Awesome. I’ll poke Betz again about more boards. Thanks!

Hi,

I would like three (3) fully assembled (#3). Thanks Tony.