You can sign up and submit your gerbers (or Eagle .brd files, up to version 6.2.0) and it will do some analysis, determine the cost (it's still $5/sq.in. for 3 copies), and show you each of the layers (rendered with the classic purple color, where appropriate). It will save the projects you submit (presumably, to allow easy re-ordering?) and the payment processing is all on the same site (paypal or google checkout).
I've used Laen's service in the past, and it's been really good. This looks like a major improvement, I've just submitted my first order, so we'll see how it all turns out.
I just put together my XC95144XL CPLD Breakout board. This is much like the XC9572XL, but with twice the macrocells.
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Observe the sideways SMT-A package 10uF tantalum cap on C14 -- I can usually put an 0805 cap on 0603 pads (or vice versa) but there was no way this was fitting. I did manage to connect the pads once I put it up and on its side a bit.
I didn't populate the top headers -- I forgot to include them in the order with the IC, and didn't want to wait for another order to come in. The TQFP-100 package was really hard to solder this time -- the first time I tried it, it didn't line up as well as I thought, so I had to redo it all with my hot air rework station. I also skipped the external clock. I have one more of those crystals, but I've had a lot of trouble soldering them on, so I thought I'd wait until I needed it.
I'm going to try to work through some of the tutorials to make sure I can get it to work. Maybe with this one, combined with the other, I can get that discrete logic I2C thing working...
[quote author="arakis"]the Q2 part of the circuit should work, the q3 seems there is no way for it to work, 'cause when the multimeter is connected, with load at near to VCC, S,D,and G will be at the same potential..[/quote]
You're right, of course, I wasn't thinking about this.
[quote author="arakis"]how about using a high side Pfet for q3, that is driven with an nFet...(gate connected to the same gate as the q2, source and GND, drain at the gate of the q3 pfet(wiht a pullup there as well))...when there is a multimeter, this will turn off Q2, and turn on the nFet, whic will turn on the Pfet..,
when there is no multimeter connected, the q2 will open, and the NFET will shut shut down, this will leave the q3 pfet pulled up and it will shut off[/quote]
This is what I ended up doing, and it worked. There was still a small difference in the voltage to the circuit, but it was only a 5mV or so.
[quote author="arakis"]P.S.S another thing, youll need a rectifier diode between the junction pint and the q3,to prevent current going into the q2 gate when there is no multimeter[/quote]
The need for this goes away when I use an NFET to drive the PFET.
[quote author="arakis"]Just thoght of even better solution, insted of the q3, just place a shotkey diode...when there is a multimeter, the current will flow through it and shut off q2, like you envisioned...when you take the multimeter off.. PMOS is switched on and the diode is reverse polarized preventin revrese curent to shut the PMOS off...
PFET..Drain at the and terminal of the multimeer and the gate of the q2, Sorce at Vout....and GATE to gnd...[/quote]
A Schottky would probably work, but it would give me more of a voltage drop than I was looking for. The first thing I tried, actually, was the last thing you suggested, the PMOS-as-ideal-diode. It works well for the reverse-polarity-protection case illustrated in that post, but it fails for the OR-ing case I need there. Because the gate of the Q3 PFET is always at ground potential, when the multimeter is *not* attached, the Q3 PFET conducts back from the vout to the gate of the current-passing Q2 PFET, which starts to choke off the voltage going through. It reaches a steady state around 3V or so on the output.
[quote author="arakis"]I also recommended using the u current setup, INA138, 139, 169 and 168 from TI are really cheap high-side current shunt monitors.. and the setup is simple as 2 resistors and a small sot23-5[/quote]
I have some INA169s around, and so I will investigate this approach next. I really like the idea of leaving the current sense resistor in there, that way, the output voltage will not change (possibly disrupting the load) when adding or removing the multimeter. I will experiment with this. If it works, and the cost difference isn't too huge, I expect I'll go with it. (I've been thinking of making a small production run of PCBs or kits if I get this thing working).
I just realized I could also follow Dave Jones's microcurrent approach, and put a current-sense resistor and amp in there with the right gain, and use the multimeter voltage probes to take the measurement.
[Edit:] But I'm still very interested to find out if there is some approach that would work like the one I was exploring.
After implementing the PFET fuse-tripped indicator, I had some ideas about a way to auto-switch for current measurement (rather than using a jumper, as I did above, to switch between a multimeter and a bypass).
My goal was to have a circuit with two test points that would work normally (i.e., pass current) when nothing was attached, but when current-measuring multimeter probes were touched to the test points, the circuit would disconnect the bypass and switch all current through the multimeter. I was hoping that this would make current measurement as non-disruptive as voltage measurement.
Here's the circuit I came up with. It doesn't quite work, but I think I know why, and I will solicit suggestions for improving it, since I'm not sure how to fix it.
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The idea is that Q2 (PFET) and Q3 (NFET) would take turns passing the current whether or not the multimeter was connected to the test points. If the test points were left unconnected, then R1 would pull the gate of the PFET down (with respect to the drain), causing Q2 to conduct, and the gate of the NFET down (with respect to the source), causing Q3 to not conduct.
When a multimeter is connected in current-sense mode, it (effectively) shorts the two terminals together. This overpowers the pulldown resistor, and brings the gate of the PFET high (with respect to the drain) and the gate of the NFET high (with respect to the source), which causes the PFET to stop conducing and the NFET to conduct through the multimeter, allowing for current measurement.
The problem, I think, is that this design requires ideal switches that are perfectly on or off, and that any MOSFETs I might find will probably never make it out of the linear region, because the voltage difference between the gate and the drain or source will never really be large enough to put the MOSFET in saturation. The MOSFETs will then have a substantial voltage drop across them, and I won't get the output voltage I want available to the load.
So, my questions are, is it just a matter of finding a high(er) performance FET to use (I'm using an 2N7000 for the NFET and the same higher-performance PFET as the indicator circuit)? Or should I look for some kind of other switching semiconductor (like a switch IC? A transistor would have more of a voltage drop between the collector and emitter than I would be looking for (I think). Or should I look for a different circuit entirely? Or should I give up on this, because it can't be done? I'm worried that anything more complicated would end up not being cost effective.
Yeah, I saw that on the Wiki, it looks really handy. I was designing my own for a while (with current limit and measurement) but the project has languished.
I'm having trouble isolating a short-circuit on one of my projects, and I keep going through fuses (it has its own transformer, rectifier, and fused AC input). I wanted a resettable fuse board so I could figure out what was causing my blown fuses.
Here is the board I came up with:
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It's got terminal block and USB B connector input, terminal block and USB A connector output, a terminal for multimeter probes (for current measurement) and a bypass, a "power good" indicator LED, and a "fuse tripped" indicator LED.
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The "fuse tripped" indicator is the most interesting part of the circuit (to me, anyway). The P-channel MOSFET source is on the near side of the PTC, and the gate is on the far side of the PTC, pulled down to ground. When the current through the PTC is less than the trip current of the PTC (250mA), the voltage drop across the PTC is negligible, and therefore the voltage at the gate is high with respect to the drain, and so the PFET does not conduct, and the LED is dark. When the current through the PTC exceeds the trip current, the resistance increases dramatically (and with it, the voltage drop across the PTC). Then the pull down brings the gate voltage closer to the drain voltage, and the PFET conducts, lighting up the LED.
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Because I wanted to be able to handle large voltages (~40V, max), I used 3x 10k resistors in parallel, for a poor man's 3k3 high(er) power resistor, to avoid exceeding the current limit of the LED. I was worried that they would be too much to light up well when using the 5V from the USB connector, but I tried it out, and though dim, it is visible.
Now I have something I can use for in-line current measurements for USB-powered projects (or chargers, or whatever), and I can limit the current to less than the 500mA max provided by the USB spec (yes, I know that high power devices are supposed to negotiate high power usage with the host...). I hope it proves useful in isolating the short in my other project, we'll see.
It was a lot easier than I thought, the most nerve-wracking part was after submitting the initial gerbers (without the patch that drew the entire board outline) and getting a response from Seeed saying something to the effect of "are you sure this is what you wanted? without a board outline you will get 2x the order, and we will charge your card for it. give us corrected gerbers ASAP".
I'm glad you found it useful. I won't mention how this instructable's entered in a contest, nor how you can go vote for it, if you find it worthy, very easily by looking at the banner near the top of the page. That would be rather gauche, wouldn't it?
There are hex files for 644 and 1284 bootloaders in there, and I am pretty sure those are the ones I used (I loaded them some time ago, and I don't remember...).
I hope that helps some. Glad to hear you got it put together.
I have been putting together my free Programmable Load PCB, based on this design: http://dangerousprototypes.com/docs/Oth ... Dummy_Load, and this forum thread: viewtopic.php?f=19&t=3532 [attachment=2] I failed to add some of the parts to my latest order, so I had to make do. I used an 0.1ohm 1% 3W power resistor for R4, and an MTP3055 for the power MOSFET. Here's my makeshift PTC resettable fuse. It can only handle 250mA, so I want to retry and upgrade it sometime. The current sense resistor and the MOSFET should easily be able to handle up to 3A.[attachment=1] Here's a hack to attach a switch I had, which fit okay, though it hangs off the edge of the board. You can also see the power jack, which works, but the programming header is in the way, I'll have to adjust it.[attachment=0]
That forum thread shifted to another topic, so I made a new one here, for my questions. I think I get the general theory of the design, but I am not sure on a few of the resistors that were not set up in the BOM. Can anyone explain what purposes R2,R3,R5,R6, and R7 serve, or what values I should use? I'm kind of a greenhorn with this kind of analog stuff, know that there's no current that flows from the MOSFET base to the drain, so what does R3 do? Does it introduce a voltage drop to reduce the voltage at the MOSFET's base? I know R6 sets the gain for the opamp providing the voltage drop over the current sense resistor to the PIC, but what kind of gain should I use? Do R2 and R5 set some kind of scaling? Any feedback would be helpful.
Finally, does anyone have an example firmware for this project? I was going to try and cook something up based on the LCD backpack firmware, if I can't find anything else, but a better starting point would be great...
The main changes are better prototyping area (separated from the MCU pins) and more power rails. I also put the auto-reset circuit in (now that I have an FTDI basic that uses the DTR pin to trigger it).
I just wrote up an instructable (here: http://www.instructables.com/id/Paneliz ... ree-Light/) about how you can easily panelize PCBs for SeeedStudio's Fusion PCB service. I thought it might be of some interest here, especially considering that they are currently offering 10 count 10cm x 10cm PCBs for the same price as 10 count 10cm x 5cm PCBs.
It requires a minor patch to gerbmerge, but after that, it works like a charm.
I made this a while ago, but just busted it out, and hadn't yet posted up a photo of it. I added the optional 20MHz xtal to the back, to use as the global clock. Also, I only had a 6mm switch, but it seemed to (kind-of) fit, and it works okay.
I love these CPLD breakouts, they're so simple (hardly any support circuitry!), but they can still do a lot of interesting things.
It uses a PIC24, but you might be able to mod the firmware to work with the PIC on the IR toy.
I'd be interested in what you come up with, I was stuck in the pediatric ER for a few hours yesterday with a horrible late-night Disney channel show on, and no way to turn it off.
