prototyping PCB for SO-8 opamp? - Page 1
Forum section: electronics / projects

author: JBeale
author_rank: Frequent Contributor
timestamp: August 14, 2017, 09:09:12 pm
content: Most modern opamps come in SO-8 or smaller packages. Many of the single-amp SO-8's use the same pins for power, inputs and output. I want to build a simple noninverting amp with a single opamp in SO-8 package. I only need to use 5 pins (2,3,4,6,7) on the SO8. I've already tried the generic SO-8 to DIP adaptor boards in turn mounted on a 0.1" breadboard, but it's sort of cumbersome, and I would also like to make the whole thing a little more compact.This DEM-OPA-SO-1B opamp prototyping board from TIhttp://www.ti.com/lit/ug/sbou026d/sbou026d.pdfis almost what I'm looking for, although it's a bit large and has pads for SMA connectors which I don't need. Is there anything like this but simpler, with just simple pads or through-holes for the power & signal connections?I can do my own PCB layout and maybe will if I can't find something, but it takes time and a simple SO-8 amp prototyping PCB seems like it should be useful enough to be already available (?)

author: CopperCone
author_rank: Super Contributor
timestamp: August 14, 2017, 10:08:13 pm
content: you can superglue it upside down (just a drop! or use hotglue) and solder fine wires to it (like kynar wire). Its a pain in the ass but if you get tweezers, use alot of flux and put solder on both the opamp pins and the wire first (single strand) it will work.You just have to be patient. takes some skill and you will feel like a chimpanzee trying to catch ants from an ant hive with a bent stick at first but it works. I can do it pretty quick now.You should measure / prepare the wires first so you don't have to strip/cut them after the weak solder connection is made. Sometimes its better to solder them to the PCB first, THEN solder to your chip, to minimize stress on leads (assuming you want to reuse it)You also need some fine tools (i recommend swanstrom pliers) to manipulate the wire after it has been soldered (that is, you want to grab the base of the wire prior to bending as not to stress the part lead.It cleans up easy too with some flux and copper solder wick.depending on how patient you are, and how fine your soldering iron is, how thin the wire is, and magnification, you can pretty much do it to any part... however for really small shit you will probably need to make jigs. soic 8 is doable by hand with no magnification if you have alright vision and steady hands.. a soldering laser would probably come in real handy for some of these small parts, with flux. and possibly a ultrasonic cleaner to inspect them with afterwords (removing flux crud).good flux is important here. I recommend a orange/yellow jel one... the water clear water thin 'no clean' kind of sucks for this.

author: KL27x
author_rank: Super Contributor
timestamp: August 14, 2017, 10:40:42 pm
content: I would guess that 8 pin dual opamps are even more standardized in the pinout. The single opamps often have some variation and/or extra pin funcitons.Just googling "opamp breakout" you can find a couple different kinds on ebay or amazon. Here's one from Sparkfunhttps://www.sparkfun.com/products/9816

author: JBeale
author_rank: Frequent Contributor
timestamp: August 14, 2017, 11:01:25 pm
content: Thanks for that Sparkfun link, that is the kind of thing I had in mind. Somehow my google searches didn't find that one. Looks like it comes with the LM358 already installed. I want to use a specific low-noise opamp so for now, I will make do with the TI board DEM-OPA-SO-1B

author: JBeale
author_rank: Frequent Contributor
timestamp: May 28, 2021, 07:05:04 pm
content: Coming back after some years to follow up on this post, I found that TI also has a PCB panel with an assortment of SOIC (SO-8) opamp layouts includinginverting and non-inverting amp, active filters etc. This is even closer to the thing I was originally looking for. Ideally you could get a set of just amp layouts, but they only sell the full variety-pack panel.https://www.ti.com/lit/ug/sbou162a/sbou162a.pdfhttps://www.digikey.com/en/products/detail/texas-instruments/DIYAMP-SOIC-EVM/7563133

author: girishv
author_rank: Regular Contributor
timestamp: May 29, 2021, 11:53:11 am
content: Quote from: JBeale on May 28, 2021, 07:05:04 pmCheckouthttps://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/789387/diyamp-soic-evm-and-dual-diyamp-evmYou can download the layout and replicate only the ones you need.

author: Nominal Animal
author_rank: Super Contributor
timestamp: May 30, 2021, 03:22:15 pm
content: It would be so nice to have a sticky in the Projects, Designs, and Technical Stuff section, with links to or attachments of Gerbers for useful prototyping boards (freely licensed) one could adjust and then order off PCB manufacturers. Like the Analog Filtering one, but with free-to-use prototyping boards.I have afew, but me being a butterfinger hobbyist, I cannot vouch they work.. The one-sided 0.8" × 2.2",0.8mm pitch TQFP-44 adaptermight be useful. I'd love to see prototyping boards for digital isolators and fast optocouplers, and for high-side P-channel MOSFET switches (for switching DC current for other devices), for example. Or an instrumentation amplifier, so one could experiment with e.g. current sensing using built-in ADC.The key being, some of you resident EE's here would occasionally take a look, and point out any deficiencies in the design, and make suggestions on how to make them better.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 30, 2021, 04:10:47 pm
content: you could make a so-8 adapter pcb to an 5 pins inline pcb (single row pinout) ??

author: Nominal Animal
author_rank: Super Contributor
timestamp: May 30, 2021, 07:41:13 pm
content: Quote from: coromonadalix on May 30, 2021, 04:10:47 pmSure; wouldn't be more than a few moments at say EasyEda. You could even make it 6×4 pins, so it sits at the edge of a breadboard, takes power from the power rail, and exposes all six pins on the breadboard, while only taking up one row of pins. Or 5×4; I'd only need to know what's a typical pinout. Perhaps one pinout on one side, and another on the other?Here is a practical example (in public domain):A dual SN74LVC8T245 voltage level shifter to sit next to a breadboard. There are a total of 16 unidirectional lines, with two slide switches to select the direction of each group of eight signals. Each side has a separate VCC, which can be anything between 1.65V and 5.5V. The data pins are on 0.1" pitch, and one can solder either a flat cable (8 lines out of a 10-pin rainbow cable, for example), male headers, or female headers to it.I am thinking a smaller variant with fixed signal directions, but completely isolated using a digital isolator (ADuM, Si86xx, ISO76xx) separately powered via two isolated DC-DC modules (say, using an USB connector, for use with power banks) would be even more useful. The modules are needed because the isolators often require a 3.3V or 5V supply; two are needed, so that the two sides' grounds are completely separate. This would be useful when playing with motor controllers. Needs thinking.

author: Nominal Animal
author_rank: Super Contributor
timestamp: May 30, 2021, 10:29:06 pm
content: And here is what I'd like to see in a prototyping PCB for an SO-8 opamp:Both are single-sided, and use the pinout I found for a few opamps. The right side one is the truly simple one, whereas the left side one includes SMD pads for a bypass cap between V+ and V-, and pads for an SMD 20k trimpot for adjusting input offset (for opamps that support that); it is intended to sit on protoboards where the power rail is 0.2" away from the top row, and aligned with the signal pins. The left one is a funky shape just so that it wouldn't take more than three rows of data pins (but is still one-sided). Both designs are in Public Domain.What I do not know, is whether these are considered useful or not. I'm just a hobbyist, and don't have the real-world practical experience to tell.

author: Nominal Animal
author_rank: Super Contributor
timestamp: May 30, 2021, 11:55:48 pm
content: And finally, here's my prototyping PCB for TinyLogic (NC7SZ57 and NC7SZ58) in SC-70:The TinyLogic IC can be soldered on either side of the PCB can be used; the difference is just in the layout. This, too, is optimized for specific breadboard types, either with power rails aligned, or with a 0.050" offset (I have both these types).

author: coromonadalix
author_rank: Super Contributor
timestamp: May 31, 2021, 01:18:52 am
content: Sometimes keeping an 0.1" spacing / pitch for pcb is not optimal, you loose tons of spaceI had to buy an 6 pin dip adapter for a mere sot-363 ic, doesn't exist in dip packaging, and the pins under it are bend alternatively left and right .... Chipquick adapter model PA0087A mere 3,47$ CAD for them x32 = outch lollI had to rapidly design 32 boards in dip pinouts ... and the adpater look like a monster on the pcb's lollThe previous threads pcb designs are nice