What are people's favorite BLE modules? I have been out of the game for a while.
Looks like there are plenty of slave modules but it would be better to not need a second microcontroller as most run a Cortex Mx or similar inside anyway.
Best for me if it is already FCC or similar certified. I have found a few and am digging now but the software stack use with custom firmware seems a bit muddled on everything I have found so far.
Does anyone know off hand what if any packets a phone associated with some wifi network sends if it does not hear a beacon? Some SSIDs are not broadcast so it might send something even before it hears the router/base stasion. I've started to look but have found out yet... If anyone knows it will save me much hunting.
I just noticed the the guy who gave us Freerouter has posted a notice that he has had to remove the router software from his website.
This is big news at least for KiCAD users. So if you haven't routed a PCB in a few weeks you might just have noticed as I have. He had open sourced the software a month or two ago which might have actually prompted this confrontation, though I have no idea honestly. I have been using this software a long time and it is sad.
The source is still available as of right now, and directions on its compilation still exist on the Freerouting.net forum at the moment.
Sounds like he will get legal advice from a lawyer paid by the FSF but just on how to mitigate this heavy handed attack by his former employer, who I have to presume believes it owns the code because it does a similar function to the one he wrote for them? I don't know the details really.
It is important news for the maker community. Luckily for use things like trace length matching now look to be in alpha development for KiCAD so the need for freerouter might go down some as things move forward.
I need to find a solution for solder free connection between a normal 0.1" double row header and a second board. The second board can be soldered but the first cannot. I know of pogo pins but it would be better to have something more like a snap in where the pins flare out radially to make contact into the holes.
I've been sniffing around digikey for a bit but so far nothing as I don't know what they are called. I think I saw something like this on a teardown of an airbag sensor on eevblog. Any pointers would be most appreciated.
I am starting work on a new project, in principle, today and have started ordering parts to put my plans into action. Its easier to change things on paper than in copper so I thought I would be more transparent in my development process this time, hopefully people will have some thoughts.
The goal is a: high quality, minimum cost, easy, open, networked audio player.
I still like my stereo but the lack of convenience of physically loading discs into a significant. I also obtain digital music sometimes just MP3s sometimes FLAC that does not have physical media to play. High quality audio interfaces exist for PCs and in USB form but don't meet cost/size/power requirements for my living room.
I could put this on hydrogen audio or some audio forum but I think sadly that will result in a lot of FUD. I won't belabor this point but when RF designs are done badly you almost can just look at the board and say yep that person doesn't know what they are doing. Audio is more forgiving and less. To obtain very high performance is hard, to obtain what most people won't hear a difference between is pretty easy.
As some of you might know I had started a project years ago called openHiFi. This was based on a LM3S part and Wolfson DAC. The first prototype worked okay. The software got to a point where I could index a 2.5" hard drive and play any FLAC track on the disc with a serial command. It needed more work though. The digital board produced measurable EM radiation. This was down to it being one of my first PCB designs and a fast number of fast single ended traces on a cheap 2-layer PCB. Fast forward to the present I still have the same desires for a home audio player with an open testable design.
Much of the burden of completing openHiFi was the need for software. When Raspberry Pi came out and then BeagleBone Black, I realized that for non-realtime small volume microcontroller boards like Procyon (on which openHiFi was based) were likely not the best solution. Software ease trumps the slightly reduced cost easily.
With this realization I started to brain storm some options. One of the things I have noticed about consumer hardware is that they do not take audio too seriously. Most cell phones I have had after the cell phone/MP3 convergence sound subjectively worse than the stand alone players that proceeded them. Raspberry Pi is not known for its stellar output from its audio jack. For a long time I2S was not available without a hack. Now it is. I2S is also available on BeagleBone Black (BBB) in principle, though I have to test it, on the black this appears to be fed to the HDMI framing chip. Since those I/Os are sent to the pin header as well it may be possible to simply tap them. I looked extracting audio data from HDMI, while 3rd party boxes do this they generally create SPDIF streams which have worse jitter problems than I2S. Getting access to HDMI directly requires fees I believe.
Jitter may also be an issue with the I2S streams on the Pi and BBB. On the Pi only there is no MCLK output...
Even when I2S exists on a chip as I said jitter on the clocking can make it less than ideal, often times it does not exist, but SPI almost always does.
This consideration led to the formation of an idea of an FPGA based SPI to I2S converter. A CPLD might work as well, but given latencies in the driving I decided buffering would be required to no drop samples. The idea is simple. To minimize phase noise use switch crystals at the true frequency of the stream being output. Support only the common sample rates force resampling of everything else in software. Send the data to several RAM buffers on the FPGA using fast-SPI with a simple 0xFF return for when the buffers are full. This design should practically eliminate jitter, though of course anything produces some jitter and the FPGA is no different, but in principle this may be close to as good as can be done short of an ASIC. At this point I was assuming I would be writing the software as well. I figured I would create a little C program that would handle the streaming to the SPI port in software. Then there would be a need for a software interface to play the files.
The primary author of this project is clearly plugged in to the DIY audio community and he makes some recommendations on USB DACs to use. The most interesting of which is ODAC.
This is an interesting project and as an engineer a breath of fresh air. Objective measurements are always best. Always. You can like whatever coloration of music you want but an objective output + digital processing before rendering should get you any type of sound you want, that's just math. So our goal in producing audio equipment should be objective output with the best possible performance we can manage. The ODAC documentation seems legitimate because it actually tells you very important things like the effective number of bits the board actually is capable of. You can very very easily take a 24-bit DAC and produce 14-bit effective output.
I read every post this guy made about his ODAC design and for the most part it reads well. Apart from jitter on the I2S stream feeding the DAC the other big issue with high resolution DAC stuff is likely going to be the power supply. The creator of the ODAC claims that he has filtered the USB power in a clever way and this let him run it from the USB power. My reply to that is maybe, but the performance of this design is going to be pretty dependent on how good that 5 V power rail actually is.
Thankfully the schematic was published: http://http://www.yoyodyneconsulting.ca/downloads/General/ODAC/ODAC-release.pdf. From this we can see the filtering is not actually that sophisticated. It is just a second order filter and a LDO with a first order output filter. This is the first thing that makes me nervous about taking everything the guy wrote as fact, though I honestly suspect it is. The method however cannot reject high frequency components very well. These are generally above the close loop bandwidth of the LDO and above the self-resonance of the passives. I don't know the later but the former tends to be < 100 KHz depending on the LDO. This may mean these frequencies are not audible but we must remember that any non-linearity will cause mixing and so the high frequencies can be downmixed to audio frequencies. Given the extreme dynamic range specs of audio one must be careful.
The creator of ODAC to his credit spends considerable space discussing the power supply issue, and suggests a worst case remedy of a powered USB hub. This is a fine solution if the powered USB hub's power supply is clean. The other general issue with power is that bad power supplies can create noise on the mains and this can feed into the power supplies of other items. There is no perfect solution. A nice linear transformer though will likely have poor transduction of these high frequencies and the 50/60 Hz and harmonics are not hard to filter.
So if you want an off the shelf solution to me it looks like ODAC + a PCB to let it run off a linear power supply would be a pretty nice one. This would cost over 200 USD though when it was all said and done. Eeep. Given the DAC on ODAC is a 4-8 dollar part this seems excessive.
It also seems a bit silly to have access to an I2S and not use it, instead to use USB transport and then go back to I2S. Its okay in that jitter performance will then be computer independent but it is not ideal in terms of cost. The 200 dollar solution also can be reused. These are good things but it would be nice in my view to have a solution that honestly was affordable and pretty good. Maybe not quite as good as the ODAC but maybe it could be just as good.
Some look better executed than others but all have things that concern me. The DAC choices seem to be fine. The most common seem to be PCM5102A and ES9023. The later seems more interesting to me because of jitter reduction that may be inside with an asynchronous MCLK (http://http://www.esstech.com/pdf/about-jitter.pdf). It is hard to tell just from the datasheets what patents it is implementing. The fact that PCM5102A uses a PLL to create MCLK when not presented with a synchronous one makes me think it would not be good at rejecting BCLK jitter. To do so would hurt the stability of the lock in the PLL. It is possible that the loop filter is cleverly designed. But inherently the integration time has to be short enough for it to remain locked or samples will be lost.
Today I made some simple measurements on my raspberry Pi's BCLK output with my HP 8495E spectrum analyzer. I found the center frequency of BCLK was 1.411251 MHz on a 30 Hz RBW. It is an error of 36 ppm, which is probably just the crystal tolerance. Phase noise is a bit trickier to measure well. A causal estimate with random power supplies is that it is about -54 dBc/Hz at 100 Hz, which is certainly plausible with regular XO clock modules. It is probably better than this though. I'll have to think on how to do a proper measurement of the phase noise.
So to conclude this first post, it I think it would be fun/neat to try to develop a DAC that can be driven by BBB or Pi and uses the Volumio software. It would be nice to measure it objectively as it is developed. I don't own the equipment to do this however.
I feel like most projects on DP are digital, save for maybe some audio stuff. I am wondering how many folks work on analog things and if there is a need in the community for signal sources or other analog test gear that might just not be affordable?
Digital stuff is far less expensive to manufacture and design. I guess the SDR stuff is analog but largely it is re-purposing USB Rx designs with new software...
I've been working on creating a power supply for supplying nice clean delicious bipolar power to things that need it.
Although I have several lab power supplies any sort of instrument I create that needs to be DC coupled needs a bipolar power supply (unless the signal DC part of the signal is positive definite).
I don't know how many others would need such a supply, and while I tried to consider cost in the design I mostly considered performance. (Chime in if you need them something like this badly).
In some ways this is the worst of both worlds of linear and switch mode supplies: it has to get its DC input from a linear supply so it has the efficiency of a linear supply, and it has a high part count because it is a switcher. It does avoid people getting electrocuted though, which is very important.
It still needs testing under heavy load and I may remove the barrel input and make this a pure slave module for projects before the design is finalized. I am pretty happy with the performance so far.
I have some projects that will have off board power supplies. Historically one of the issues with these guys is that the connectors are so expensive that I often have just used 0.1" headers. We are talking 0.5 A at most here at 15 V.
Any tips for cheap good connectors for this sort of task. Of course there are lots of things from Molex but again just not ultra cheap. It always seems cable assemblies are pricier than they should be. I'd like to have at least 4 rails so 8 wires perhaps. Min 4 wires for 3 rails with 1 COM.
Thanks for the useful suggestions in advance.
PS: Must have a real supply source (thus probably not an ebay thing).
I am interested in some projects that would require large data transfers, and although I am aware of some USB 2 micros (Atmel M3 and ST M4s etc) I am not sure if there is a good USB stack to back them (the more open the better but more documentation is the most important).
Also I am not certain what class is typically used for such transfers. Mass storage seems the most common bulk transfer class but I am not sure it is the most appropriate. A very fast serial ACM like thing would be easiest. I seem to remember you can have more than one class on the USB port though, like mass storage + ACM.
In short I need to essentially stream MB/s with commands embedded over USB. Any software/silicon suggestions (other than FTDI) are welcome.
I know some folks who have built RepRaps. I've seen some older makerbots. I've had things printed via laser sintering.
But I have never had the chance to do apples to apples. Someone might tell me their RepRap requires too much aligning, another might be unhappy with the layer thickness or sanding.
I think it might be useful if people in the community, particularly those who have used more than one type for similar things could share their experiences.
For instance how brittle is PLA really? Do certain manufactures sample prints look way better than what you got? Does your printer need work all the time?
It pretty hard to judge this stuff, we now have printers as cheap as 500 dollars and still have ones that cost 20K or even 100s of thousands. Where is the value, what drawbacks do you see?
Finally thoughts on what CAD you like would be useful. I know many use sketchup but I never found ways with that to draw precise sizes, and with its sale I'm unsure of its future.
As I posted on my blog I'm going to shift teho Labs away from development boards. When I started teho Labs there were no ARM development boards for M3 that $$$ particularly using Ti's line. Now we have STM32 discovery and M4 Launchpad.
Procyon remains in a useful space but with Raspberry Pi there is less room to use it as well.
Basically there isn't a lot of room for a small volume company in this space anymore I don't think.
Anyway the point of this post is I want to clear the stock of boards I have. And I want to do this before I move to take my new job.
I have a hand full of Eridani's that need rework. I don't however have the time to do the rework, basically if you have the ability to desolder a LQFP64 and resolder it you should have no issue making them work. You'll also need an ARM JTAG (Bus Pirate should work with openOCD).
If you want a board PM me with an offer. It can be money or a cool project. US is strongly preferred both for cost of postage and also the customs form overhead.
It is a GPIB adapter, I've long though of making one and there was some activity in the forum on making home built ones.
Before I start a project though I carefully think about all the parts that would be needed to finish it. The electronics could be almost any micro. Getting a low cost hardware box is an issue though...
The screw is M3.5x0.6 threaded (see wikipedia). All the commercial GPIB adapters use these long knurled head thumb screws.
I checked the usual US suspects like electronics suppliers and McMaster Carr nothing. Even the short ones I found were very very pricey.
Anyone know of a good source for such things? (Good = long term business not ebay which can disappear).
Micro is becoming more ubiquitous with phones for users having cables around. Mini I think still finds its way onto cameras and HDs. Full size is still on printers and things it seems. Anyone know any printers that don't use a full size?
