I like your approach. The main reason I wanted this was not for the breadboard, but so I'd have "standard" I2C and ICSP connectors that I could connect directly to other boards (without using the breadboard to break everything out).
Also, I didn't have a spare 10-pin cable I was willing to sacrifice. I really don't like the 10-pin test clip cable that I got to go with the BP, they don't stay on well and are really hard to use. If I get really fed up with it, maybe I'll sacrifice it for something like this.
Inspired by the "Squelette" featured in Make vol. 23, I have decided to build my own basic chip amp.
The Squelette is based on a +-12.6V, 2A power supply and LM1875T amplifier IC, with basic support circuitry, delivering ~11W per channel. I want to get the most basic possible setup up and working (line in, pot for volume control, power supply, amp circuit, speaker output), but I think if I design it properly, there will be plenty of possibilities for updating things later, for instance, replacing the manual pot with a digitally-controlled pot, adding a digital tone control, adding LED visualization, integrating WiFi-router-based internet radio, and so forth.
If I put each part on a separate board (power supply, amp, control circuit) with appropriate interconnects, I think it should be relatively flexible for adding additional parts, one piece at a time.
I'm imagining a minimal front-panel interface, with a single knob (with a push-in switch) and some LEDs or a character LCD for providing feedback. The first update I want to make is replacing the volume control pot with a digital one, driven by a rotary encoder and a microcontroller. I'm looking at Maxim's DS1881.
I have no experience working with analog signals in my circuits, and would be grateful for any reading recommendations on the topic. In particular, the following questions are still hanging out there:
* Would I regret attaching a 7805 or other voltage regulator to the +12.6v output of the transformer, with no comparable load on the negative rail, to drive the microcontroller and displays? It seems like it would put the power available on the positive side of the amplifier out of balance with respect to the negative, which can't be good. On the other hand, if I'm drawing little enough current, maybe it wouldn't be a problem. Where might I expect to notice the effects? 50mA? 200mA? I think my alternatives are to put in another transformer in parallel to power the control circuitry, but I want to avoid this if I can, because that would take up a lot more space inside the enclosure.
* I want to design my own PCBs for this project, instead of just using protoboard, but I understand analog circuits are much less forgiving of noise and other things determined by the PCB layout. Are there any particular recommendations for guides or caveats for designing boards for analog circuits?
I'm working on the schematics for the basic starting elements, so I'll post those when they're ready.
The parts are on the way, so when they come in (and when I have time) I can experiment a bit and see if it will do what I want. If I can't get enough current to drive the TRIAC and the display, I'll have to go back to the transformer idea. If this works, though, it should cut down my enclosure size requirements quite a bit.
I also really liked this guy's use of the IEC C14 connector, I have a ton of old powercords that match that, so if I can find the right socket, I think that will be a much better approach than just cutting up and extension cord and sticking one end in the enclosure for my AC power.
My original goal was to avoid using a transformer entirely, for the space that they take up. The more I read about transformerless supplies, the more I think they aren't right for this project. It seems tough to get moderately high current like the >200mA that I need to drive the relay, and every bit of information about them is plastered with warnings about dangerous voltage being non-isolated and so forth. Since this is meant to drive a set of user buttons and a display in addition to the relay, I think I need to be concerned with isolation.
Since I have had little experience with doing my own AC-DC conversion, I'd rather bite the bullet and try and find a low-profile transformer I can squeeze into the enclosure. Another possibility is to get an on-chip isolated DC-DC converter, but that doesn't solve the current supply problem.
I tried using the 6-pin SPI/ISP connect, and there wasn't enough room to fit the tab on the side of the connector (which should be facing the center of the board) next to the 10-pin bus pirate connector.
Removing this tab (I used an Xacto, but a Dremel would do, too) leaves just enough room to plug both in. I'm thinking of releasing an updated version with a little more clearance between those two banks of headers.
I've also been thinking of (preemptively) updating it to make a BPv4 version (which has 12 pins, instead of just 10).
Tip : When making a new symbol, to place a bar over a signal name use the "!" character and a bar will be placed over the following characters. (ie. !EN) To terminate a bar in the middle of a signal name use another "!". (ie. !WR!/RD)
Tip : When making a new symbol, if you have more than one signal with the same name ie. GND, use the "@" character after the name and a number. (ie. GND@1, GND@2) You can use the pin number. Only the signal name will be displayed and not the "@" and following characters.
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These are two things I've wanted to know for a long time, but didn't know how to search for, and when my google-fu didn't give me answers quickly, I gave up.
I'm working on a basic relay-based controller for a yogurt maker for my wife. It's nothing fancy, the usual drill of temp-sensor->mcu->relay that applies mains power to a crockpot when necessary to maintain (roughly) the right temperature for different stages of yogurt. That's not really the interesting part.
I was thinking about powering the controller and thinking to myself "it seems kind of silly to have a wall-wart plugged in to provide power to the controller when I already have 120vac in the thing going through the relay. Now, I may be making this memory up, but I seem to remember reading somewhere recently about a IC where you hook up 120vac on one end, and it gives you something close to normal project voltages (5-12) on the other end. I can't for the life of me think what it might be called, or where I read it. In my searches, I've come across things like "flyback converters" and "non-isolated off-line switching regulators", but it's not clear to me that these are what I should be looking for.
I need something that provides around 250mA-300mA, since it takes 200mA to keep the relay active, plus a little more to drive the microcontroller and display.
Am I making this kind of thing up? Or is it an incredibly stupid and dangerous idea? Or am I just missing the right search terms?
I made this ChronoBlot a while back, but now that I have a BusPirate, I can easily test it out, set the clock, and set the alarm (and write scripts to help with that), so I'll be updating it soon and wanted to track it on this projects forum (which I prefer to a blog; the discussion seems better).
[attachment=2]
It's a DIY-remake of the ChronoDot (first version), by MaceTech ( http://www.macetech.com/blog/node/99 ). You can see more of my attempts at toner-transferring the silkscreen layer (which turned out pretty poorly in this case).
[quote author="ian"]Nice work. I notice SparkFun's staggered pin header footprint in there. Have you used it before? Do you like it? I open have a problem with header staying straight, but I use lots of sticky-tack (poster putty?) to hold stuff down when I solder and that seems to work.[/quote]
I love these staggered headers from SparkFun. I used them for the 6-pin header on the BPv3-FTDI-0.2, and for all of the headers on the 0.3 version. The 0.2 was the first board I had produced by a fab house, and the staggered header was perfect, it held the header in just the right place without any real difficulty placing it in. This is especially handy for right-angle headers (which I think might have been the original reason the dude at SparkFun developed them.
I've used them on all of my homebrew boards, but honestly, my drilling process (drill-press with squinting-eyeball-based alignment) is not precise enough to say for sure whether it makes any difference. Certainly most of my home-drilled headers are snug, some of them, I have to enlarge (by "drilling" with one blade of my flush cutters on each side until the hole is enlarged enough)
[quote author="Sjaak"]For soldering headers I use a breadboard where I put the header in, pcb on top, and then solder the header.[/quote]
I like to do this, but depending on the placement of other components or headers, there is not always room, that's why the staggered headers are nice. I use them for everything now.
I went ahead and put something together for this: [attachment=0]
You can use a 5x2 to 5x2 cable to connect it to the Bus Pirate. I thought about making it plug right in like the other shields, but I didn't like the footprint I ended up with, and these 10-pin cables are easy enough to make.
It's got:
* breadboard breakout for all 10 pins * a power connector for providing VCC from an external source * a VCC select jumper so you can pick 5V or 3V3 from the Bus Pirate (or leave it open for external power) * a VPU-VCC select jumper, so you can tie Vpu to whatever you have selected for VCC * a 4-pin "standard" I2C header * a 3-pin "standard" 1-wire header * a 6-pin AVR ISP header (can also be used as an SPI breakout)
I ended up making it two-sided in order to route all the connections, so I will be using the DorkbotPDX pcb service again. Granted, I didn't spend too much time trying to make it work on one-side...
Once I get the boards (in a few weeks) and test it, I'll put up some photos in a blog post, and release the source files.
I replaced the vertical 6-pin FTDI header with a horizontal one, and now with a header extender (really just a 6-pin passthru header) it fits just fine in my enclosure:
[attachment=1]
[attachment=0]
I love those pass-thru headers, they work great as extenders, or when I need a normal header but only have a single-sided (i.e., homebrew) pcb to attach it to.
I starting using my new Bus Pirate to try and debug the contents of an EEPROM (the whole reason I made a Bus Pirate, actually), and I found myself desiring a few accessories that would have made it rather easier.
I am interested in designing a kind of breakout board for the 10-pin cable that would split it into a 10-pin single row header for sticking in a breadboard. I also want to put jumpers for selecting VCC of 5V or 3.3V, some terminals for connecting an external VCC, a jumper for tying Vpu to VCC, and dedicated connectors for the pinouts of popular protocols (e.g., I2C, AVR programmer SPI, 1-wire, etc.), so I can use extension cables from those pinouts directly to the devices I'm trying to use.
I thought I'd check first, before diving in, whether anyone had made something similar, or found (or solved) some problems with the idea.
One trick is that there doesn't seem to be a "standard" I2C header, though I find a lot of breakout boards (like the ChronoDot, and many (though not all) of Sparkfun's I2C device breakouts) use a GND-VCC-SCL-SDA 4-pin connector.
Along the Pirate theme, I was thinking of calling it a "Broadside" or something like that, since I am bad at picking names for things.
I have released BusPirate-v3b-FTDI-0.3, which has:
* room for a shrouded I/O header * Sparkfun's locking header rows (see http://www.sparkfun.com/tutorials/114) * more clearance around voltage regulators, for easier assembly * improved label size and positioning
I don't intend to produce any more boards, unless someone wants me to put together a kit for them, but Ifelt like these updates were worth making anyway.
