Short help request. Does anyone has Chinese T12 tip clone on hands right now? Could you please measure and let me know resistance between tip terminals, small ones at the end and larger one (tip outer shell). There should be three measurements. It would be much appreciated! Thank you and sorry for off-topic message, have no idea where question will be more appropriate.
[quote author="arhi"]6675 is not the only chip :) ... check out also AD and Linear :) for e.g. LTC2484 is 5$ and it's TC to SPI, or you want LTC2485, same thing only I2C ands again 5$ part...[/quote] Thanks for the tips, I considered them before starting with the board. But you know, it's only chips and they anyway requires board, connectors and so on. LTC6081 + LT1025 as ready-made solution cost around 10$. And important advantage of my board is that you will have 2 outputs to control peripherial via I2C. I plan to use it with I2C-tiny-USB, so just these two small boards and solid state relay - and you have reflow oven controller for example.
[quote author="arhi"]you are saying the pcb + mcu + op-amp + lm75 + other passives and connectors will cost you $5 ? I have hard time believing this[/quote] PCB - 30 @$13 (ITead) = $0.43 ATTiny25 - $1.89 (Digi) MCP607 - 40 @$13 (eBay) = $0.34 (Yeah, I have them in my drawer too, and for cheap! ;o) LM75 - @0.98 (Digi) Connectors and discrete around $1.20 Total = $4.84!
[quote author="welash"]It looks to me like your feedback in the first stage is going to the non-inverting input, but should be going to the inverting input. That is, R4 should be connected to pin 2 instead of pin 3.[/quote] Thanks a lot. I really don't understand how I could miss it; checked it like hundred times when board did not started... Thanks again!
[quote author="arhi"]yup, you copied the schematic wrong :(
btw, if you want to make i2c/spi reader for the sensor, check out maxim, they have already spi thermocouple reader with embedded cold joint compensation, it will cost you much less then making one yourself, and is already calibrated.[/quote] Oh my God, I knew it should be something stupid, thanks for the help, I'll try to correct tomorrow by cutting/jumping to test the approach.
Regarding MAX6675 - it cost $14 at digi. My board cost less than $5 - 3 times less. BTW, it's also compensated, LM75 placed next to thermocouple clamp.
Guys, I feel myself frustrated and stupid. I'm really newbie in analog electronics, and some time ago started my attempts to amplify k-type thermocouple signal using standard non-inverting amplifier. Main idea was to have cheap I2C sensor for k-type, using MCU as I2C interface for the purpose of building own solder iron driver. Unfortunately my attempts were not so successful. Luckily this topic was found and I developed small board using schematic from the very first message of this thread. The only difference is that I used MCP607 instead of MCP617, which have a bit worse characteristics, but nothing significant, as I understand. Few days ago I received my boards, soldered a couple of them and found that analog part does not work as supposed. Actually I got +5V at the output of first amplifier stage (and consequently second too).
Could anybody take a look at my schematics and explain me where I'm wrong? I tried to simulate circuit in the NI Multisim, and in simulations it works fine, as expected. Maybe it will be efficient if I measure voltages on the board (where? I don't have a clue). [attachment=2][attachment=3][attachment=1][attachment=0] Thanks for any help in advance and sorry if my message is not appropriate here.
[quote author="Sjaak"]@drug123: You are a bit further then me.. This is what I had in mind (except for the pump)
Use of the bic pen is brilliant and is prolly more ergonimic.[/quote]
Regarding bic pen: I suppose that use of insulin syringe could be even more convenient as in this case you won't need to figure out how to connect needle as there will be appropriate connection. I think it worth to try.
[quote author="ian"]Sorry about that. We wrote our own spam filter, it works pretty well, but there is no way to undo it for a new user but wait 24 hours :) I added flickr.com, but you're right, it won't parse that to include the multiple subdomains. I've added it to the to-do list.[/quote] OK, no problem, then I'll update post later.
[quote author="ian"]@drug123 - Very nice, that is also the pump I plan to use.
Here's your link, sorry about the spam filter. I whitelisted Flickr for new users now:[/quote]
Sorry Ian, it seems that spam filter update does not work because it still don't allow me to post the pisture located on farm6.static.flickr.com I even can't post the reply to your message because it contains the link :)
I have made this DIY vacuum pickup once in 5 minutes. BOM used: - sparkfun Vacuum Pump (SKU ROB-10398) - $14.95; - Medical infusion set from the nearest drugstore - $0.25*; - Ball pen - $0.10; - 12V wall adapter - don't know, have a lot of them from old hardware, suppose it is less than $5 on ebay; - Any rubber-like insulation material. I had used 2" piece of self-amalgaming rubber tape but think high viscosity adhesive or silicone sealant will do the job.
Infusion set was cut and reversed to filter incoming air using included droplet filter to keep air inlet clear. Ball pen handle was cut from both ends and then small hole drilled near the needle end. This hole is pickup/release valve: by closing it you will start the suction through the needle; when it is wide-open, air flow passes through it and releases handled part. Next ball pen handle then connected to the tubing using insulation material.
Feel free to point over image for additional hints.
* I really doubt if medical supplies like infusion sets are freely available in the US/EU drugstores, but you definitely could buy suitable silicone tubing in local hardware store and dispensing needle set from dealextreme or ebay.