ok, I buy broken stuff too to repair or salvage parts... but why would people buy solar modules with big fat holes in them?

and wow, graphite electrodes are really expensive for just being a lump of carbon

is there anything to look out for when using an op-amp to replace a simple voltage divider?

@Christoph you mean as a makeshift voltage regulator?

never heard the term "makeshift"...what's that?

I want to use the opamp's output to drive another amplifier's offset input (AD8495 thermocouple amplifier)

@Christoph makeshift is like an improvisation because you have no real better solution at hand

@Christoph why doesnt a voltage divider work there? does it have a too low input impedance?

it's simply not recommended as per the datasheet

o_O

input resistance is stated as 60 kOhm in the characteristics

input current as 25 µA

60k might be a bit low for good precision indeed... do you need that precision?

but to answer the original question, a simple opamp buffer should work fine there

I need to drive two of those reference inputs and an ADC channel. precision is important because the thermocouple amplifiers only output 5mV/K

driving both with the same buffer is likely ok too

so I connect a voltage divider to the opamp's positive input, and the output to its negative input, and that's it?

@Christoph yep, just as show in the datasheet

you could also go fancy and add a voltage reference there (which might be able to drive the ref input alone)

the opamp actually divides the output of an LM336 reference

ah ok

do you have a virgin graybeard that will trim the voltage divider? ;)

No, and I think I can get away without a VGB. Do you want to have an overall picture?

I dont think I want to have a picture of that sticking around in my head...

probably...

hm, they sent me some wrong solder iron tips the other day... I would like to experiment with different selfmade tip forms... anyone knows what materials these things are made of? It looks like copper with something like tin or nickel plated on it...

regarding that virgin graybeard: I think I can really get away without one because I measure the divided, buffered voltage with the same ADC that I use to measure the thermocouple amp outputs. So I can in a first step measure the offset voltage, and then subtract it from the thermocouple readings.

I'm looking for a dirt-cheap reliable source for PTH perf boards, maybe about 7cmx4cm (but with lots of room to change size) for a summer high school program. About $2 each or less would be great. Last time I used DX, it took 6 months for the boards to get to me. Any leads?

How many?

and where are you located?

@ScottSeidman quick search on amazon reveals something like this ... amazon.de/gp/product/B00HV51YIY shouldnt those suffice for high school projects?

you can also design your own and get them from a board house if you need a lot of them. If you go that route you can already add a layout for e.g. a voltage regulator or some such

@PlasmaHH Wow, can't believe I haven't tried Amazon for this before!

@Christoph That's an interesting idea. I suppose I could even make the exact PCB and kit it out, but that would turn a day - long project into a half day, and I think I need to keep 'em busy!

@ScottSeidman sometimes it is really useful and cheap. And in my experience the great thing when ordering from china there is that they arrive within 3-6 weeks rather reliably, whereas on other platforms ordering from china is a lottery

@ScottSeidman let them make two half day projects then!

@PlasmaHH DX has always been OK with me, until for some unknown reason these boards got stuck in customs forever.

@ScottSeidman that's why I suggested to just prepare a power supply and not all of the circuit

@ScottSeidman ah ok, customs can be a pain in the arse... they seem to have some intresting schemes here for those amazon parts, they go in bulk through to some distribution center that works together with customs. its also their return address

youtu.be/05SHAlIh0GU?list=PLW_p2qCLKw5yJSUTO_C40DUetAiK58GA9 Found the ad for this summer program.

Altium's free "CircuitMaker" schematic capture + PCB design tool is now starting Beta testing, and I got access! I am really hoping for a reasonable stepping stone between Eagle and Altium for hobbyists and the general community

@KyranF I've been following that a bit. Don't ALL the files need to go into the cloud?? That would be a nonstarter for me for anything other than hobby use.

@ScottSeidman well I was just reading on their forums, it seems they have removed the option for paid private repos, it must ALL be public, but it's ALL free. It sounds like they totally fucked up the product.. lol. Altium could have easily trashed Eagle and other free/low cost EDA programs

now that there is no middle ground, people who want private stuff are going to continue to use Eagle or CircuitStudio etc.

What a stupid idea, they should definitely have the option for private projects, even if it has to be paid for (at a small cost, maybe even per-project basis)

There seems to be a minor way of keeping things private, currently. but who knows how it will evolve

@KyranF Like how when circuitlab started they let you have unlimited schematics for free. Then they set a limit and if you want more you have to pay. But they made it such a pain in the ass to delete schematics (to get below the free limit) that I just quit using it.

@ThePhoton yeah, well I hope that there is enough abuse during Beta that the community can twist the balls of the stupid management in Altium and get this thing to how we want it - where hobbyists can create and collaborate and share designs, and the lower class semi-professionals can get a good tool for a low starting cost, and perhaps later, once they produce something and get profit, get into altium designer (with a discount offered)

and even limiting to 4 layers is reasonable too, for 99% of designs except the crazy shit, and crazy shit gets paid more, so you can afford the tools like Altium Designer

@KyranF Adding the FPGA stuff was just crazy. I hope they don't think that is convinicing anyone to pay a higher price for their tool.

@ThePhoton yes they are trying to make the end-game EDA tool/program which is nice, but making us pay $10k for it is bullshit, especially when most of us only use <=50% of the program features

@KyranF if you used more, they would make you pay $20k