Here's an idea for a fairly simple breakout board, or also just a product I'm looking for but can't find (maybe you know of one). I've recently found myself in need of a way to characterize current consumption of a battery powered device in various operating modes in order to hit an aggressive battery life budget (6 months+ off a coin cell). The best way I can think of to do this is to insert a current shunt with amplifier to convert current to voltage, so the current can be monitored and correlated with software events using an oscilloscope. I don't particularly want to splurge on a differential scope probe, especially when this kind of amplifier could be made fairly easily.
The only product of the sort I could find were breakouts for ICs with internal magnetic coupling. They're intended more for high current measurement, and are too inaccurate down to the uA range. In a low power or battery application, the isolation would be unnecessary.
So what I'm describing would be a current shunt + instrumentation amplifier + possibly a low noise voltage regulator to power it. Amplifier can be externally powered (or maybe switched to battery powered), and the ground can be tied to the DUT ground. The shunt would be inserted between the battery positive and the device. I would want a usable range of ideally 100nA to 10mA, which is quite a few decades. That could be achieved using a logarithmic output voltage, or having switches/jumpers/etc to change the sensitivity range, or even with different assembly variants to provide a mA and uA version (and could be hooked up in series in practice). To avoid having an expensive (accurate) reference source on board, the user could measure the output voltage vs. input current using multimeters at two different points and extrapolate. The accuracy would be pretty decent if the amplifier has good linearity.
I haven't done much digging on whether it is technically feasible or practical. Things like, can such a high gain be achieved from shunt voltage to output without noise problems. My expertise is a bit removed from this kind of analog design.
Thoughts? Has anyone seen this kind of product or test tool?
Has anyone experienced swings in tolerance from the Seeed PCB service? I ordered some four layer boards a couple of months back with great results. My board had several tight pitch QFNs and the boards came back with great soldermask coverage. Given the cost of the service is 1/5th to 1/10th of using an American supplier, I was amazed and excited by the results. I recently ordered another board with similar design features, but the soldermask coverage is going to make assembly by reflow impossible.
Has anyone else had a similar experience? I'm trying to trace this back to an issue with tools on my end, or a change on their end. Here's a photo of the difference, the footprint is from the same Eagle library. The process from 3 months ago is on top, the recent order on the bottom. The first set of boards came shrink wrapped in plastic, and the second set came loose in a green ziploc style bag.
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Any recommendations for 4-layer services that can beat two hundred USD for 10-20 quantity boards that are ~10cm x 10cm would be welcome. :)
Found this steal when I was in Tokyo last December. I was in need of an LCR meter for a project, and had been researching my options online. I was in Akihabara and saw one that looked mighty familiar. The ODM that makes the handheld LCR meter for IET Labs seems to have sold a lot to one of the best uC stores in Akiba: Akizuki Denshi. IET list price, $330, Akiba street price, 4700 Yen, or about $60. It can do measurements up to 100khz, which is uncommon in these meters under $300. Anyway, here's a link: http://akizukidenshi.com/catalog/g/gM-06264/
Wireshark is a popular open source network sniffing tool. It has a lot of commercial support, and thus has a really rich set of plugins for different protocols. Examples of LA relevant protocols already supported: I2C, CAN, Bluetooth HCI, ZigBee, USB. It supports protocols higher in the stack for BT, ZB, and USB. Would it be possible to leverage their plugin formats for the OLS client? If support for their format could be enabled, the client would inherit a rich set of protocols.
In a recent project I was working on, it would have been invaluable to decode bluetooth packets from an analyzer sniff of a UART bus.
As a hobbyist/maker/hacker/etc, it would be useful to have access to a cheap variable constant voltage/current supply. Something similar to the functionality you get with the entry level bench top power supplies. Having something similar to your ATX breakout, that provides said variable voltage/current source would be useful. An ATX supply would have enough power/voltage to build a current/voltage source from 0 to 11ish volts, at 0 to 3+ amps with only a linear regulation scheme. A design of that type would also provide a lower noise source than just an ATX breakout. Put me on the pre-order list for a two-channel version!
I haven't searched the web to see if said project/product exists, but entry level power supplies appear to be around ~$70.
Hello DP! I'm currently in the planning phase for a new project, and would find it useful in development to have a model for the human body. I know of the ESD testing model, but don't think it is appropriate for the behavior I need to predict. Does anyone know of any models used in the biomedical engineering field?
A little background: I'd like to build a touch interface for my project where the object being touched for input is an exposed piece of metal. I'm familiar with the standard touch solutions where there is a dielectric between the finger and sense pad. In those cases there is likely a cap change in the range of 3-15pF. Due to the operating environment of my project, it would not be practical to coat the metal surface with an insulator (it would quickly get scraped off). If a human finger were to directly contact a metal sense pad, how much cap would you suspect this to add? The project will have on the order of 200 contact points, so I'd like to tie 5, 10, or maybe 20 of the pads to one line (it's okay that the micro can't tell which is touched). Having this many pads together will of course reduce the ratio of finger cap to total cap, reducing sense margin. I'll most likely be using a PIC24F with the CTMU module.
I'm away from home for a couple months, so I don't have any access to tools (LCR meter), to test the setup myself.
I'd love to hear any thoughts you guys have. Without the dielectric, will the finger have an additional resistor to ground? I will be paying attention to ESD issues, and the "body discharging" that I suspect will be necessary.
Also, does anyone see an issue with soldering a copper wire to Zinc nuts/bolts?
