I figured cost and stack would be the issues. These modules ran $23 from China, and I haven't looked more specifically at the ZG2100 but it's the chip that the MRF is based off of, so if you eBay that it might return some good results? If you look at the bottom of the Uno32 page there's a link to the beta networking stack which goes through a Microchip agreement then gives you a nice zip file which contains some good examples (one called WifiScan which seems awesome). The agreement seems reasonable... it's a start in the right direction towards open source from a company who's usually quite bound up.
Even offering breadboards for these buggers wouldn't be a bad idea since they're so simple to control over SPI.
I've been working on a project with Wifi lately and I could really use a breakout board for those pesky microchip MRF24..WB0Mx wireless boards (basically any ZG2100- or ZG2101- based board). This is the first place I looked, to grab a bare PCB rather than a populated one since I already have the modules and just want to prototype without soldering tons of small wires.
Which brings me to my question... why haven't you done WiFi yet? I know the TCP/IP stack is crap, but there are open source implementations for the Uno32 (using Microchip's stack and using a ported stack) and Maple amongst other things... The modules are super cheap and I think they'd be super useful for wireless data logging or messaging or whatever.
Like arakis said, check the caps. The high frequency scream is likely because a cap in the switching circuit is blown and the frequency of switching is probably wrong...
Then again, I don't know a whole ton about switching power supplies...
[quote author="brian"]I would say the ridges (and the layer stack in general) are for diffusion purposes.[/quote]
They are, and there's a reason for the three sheets. Two are polarizer films orthogonal to eachother, and the third is a diffuser. I've done a lot of messing around with LCD displays myself, and it turns out 3m has a good explanation of the optics of LCDs if anyone's interested here (http://solutions.3m.com/wps/portal/3M/e ... optics101/).
Have you guys seen eevBlog lately? Dave made a pretty decent small psu thats quite accurate and pwm controlled. Might be good for those of us who just want something small for the workbench...
I think I decided on the Allegro ACS712. Isolation amplifiers are expensive as hell -- therefore current shunts lose their benefit. So switch to hall-effect. In small quantities, an ACS712 is like $4.50 at DigiKey, so that looks like the best and cheapest (although not cheap) bet.
Measuring 4 channels is going to cost 20 bucks this way... ridiculous. An unisolated shunt resistor would cost a few cents :(
Those current sensors are awesome, but this is the one rare application where I don't want a non-invasive sensor! Thanks though, Sjaak!
I'm trying to measure mains current and I'm having trouble picking an op-amp.
There are sooo many out there, and some are specifically for current shunts and whatnot.
Here's some details about my application: - mains is 120vac, 170 to be safe - max current is ~3A - the current plan is to use a 2W 0.1 ohm shunt resistor (0.9W at 3A)
I also have a question about isolation. The project is a smart outlet basically -- an I2C port expander triggers a relay, which has mains voltage on the high side. The circuit in the outlet (the expander and the power for the relays) is provided by a small 5vdc wall-wart. Because the whole thing is I2C, the only signal wires needed are SCK, SDA and GND. The remote controller board runs at 3.3v and the relays require 5v @ 100mA so it is necessary for each outlet to be self-powered. So, do I need isolation? On the one hand, the box is powered from that very same mains that's being monitored, but the wallwart uses a transformer so... And then since it's all over I2C, does it even really matter if that single op amp chip is isolated?
Anyway, Im looking for an op amp from somewhere with free samples for now: Analog, Microchip, TI, etc. Microchip doesn't seem to have a very good line, whereas TI has chips for current shunt monitoring that only seem to go from +80v to -16v (no 170vac). The kill-a-watt uses the same technique with a simple lm2902 so how hard can it be, right?
I used a TPS61041 from TI. As to why: a) free samples, b) after looking at a lot of circuits, they seemed to be the simplest for the price range. The 20v line only needs a few mA so I wanted to use a controller that was more suited to small currents.
This is with a frame rate of 30fps and a screen draw rate of 75fps. Not only is it $15, but with optimization (I think you get up to level 2 free?) it only uses up a meager 8% of your CPU time!
I just wanted to share a "project" i've been messing with lately. A while back I noticed some cheap ($7) 240 x 160 lcds on eBay with touchscreens. Obviously I had to buy a few of them. Since then, they've just been sitting on my desk shelf downstairs. Just recently I got around to hooking one up and making a little proto board for it.
The thing about these LCDs is that they don't have a controller -- you have to drive them yourself with a higher powered processor (PIC32). Luckily, Matt Bommicino from CafeLogic did all the dirty work and wrote up a sweet site (including firmware) about how to drive these screens.
The coolest part of this is that I left my PicKit2 programmer at home, so I had to run it all from a ChipKit Uno32 using the default bootloader. As you can see in the third picture (top right corner), the code uses about 25% of the processor time. This includes a stripped-down version of Microchip's graphics library (ie clock, buttons, text, etc).
Here's the kicker: If you already have a PIC32 lying around, this thing costs you under 15 bucks to set up! A graphic lcd with backlight and touchscreen for <$20?! I'll gladly share my board layout (once I fix it up for v2) if people are interested.
Just a quick mention: most bluetooth modules don't need a logic converter. Not the transistor based one anyway. Usually, one of the lines (TX on the module) is fine because 3.3v is a logic-high for the 5v chips. The other line (RX on the module) needs a simple resistor voltage divider circuit (10k, 20k I believe) to cut down the high level to a suitable 3.3v or so. I use it on my boards and it has never failed me.
[quote author="arhi"] With regards to encasing objects like this usb device, I seen ppl in reprap community do following (I never tried myself so this is second hand talk) - they make a "mold" out of ABS/PLA, then they spray the mold with PTFE filled oil, then they fill the mold with electronics potting resin and stick the electronics in - when resin cures they remove the ABS/PLA mold. I even seen mold made for buttons and guy then poors silicon in the mold, put the metal plate on one side and when it cures he use that to make keypads for his projects [/quote]
Would you mind linking to this? Sounds realllly interesting!
