In my experience HP printers are the pinnacle of planned obsolescence. Are you sure you want to use them as a model for your designs? I’m not being flip here. Also, I’m sure they offshore a lot of this and their prototyping costs reflect this. Think of ‘economies of scale’. Your time and efforts and costs might not be as disposable.
It was a rhetorical question! 
Thank goodness we are no longer confined by the processes of two decades past!
Acid traps were a thing of the past a long time ago. Today’s processes are mostly alkaline. There are many benefits to using alkaline etching, one being a much reduced tendency for over etching such as etching sideways under the mask. As well as the ability to recover both the etchant and the copper.
An example of such a case would be very interesting indeed. 
You might, however I would read the datasheet because somebody already did exactly that.
See above! Oh, by the way, it’s 2017!
I just retired an HP LaserJet 4000 that has worked flawlessly for more than two decades. I brought it with me when I moved from Canada to Australia and needed a stepdown transformer to run it here. It was a shame as it still printed like the day I bought it and hardly used any toner. It was slow by today’s standards and I broke the cover over the toner cartridge so I finally replaced it.
They didn’t break any “rules” they just knew when the rules applied and when they didn’t.
…cause the datasheet is always right.
Sure! Again, it all depends upon perspective.
The main board that I had was fairly large and complex. If they had significant assembly difficulties I bet they would have made changes to keep from throwing that many parts away, or having a technician fix every board.
And, I did not see any obvious rework to the board.
You may want to send @Sprig the board from your 20 year old printer to study then. It probably would have been more fair to ask about the printer board he studied first. HP puts out lots of printers now days that the standard seems to be, warranty +1 day. I worked for a major manufacturer that claimed people only expected appliances to last 10 years because they WANTED to upgrade by then. Best practices are something that evolve though. In the end it is his time, money and effort to do with as he chooses.
Always? No! But usually. In fact I am currently in communications with a manufacturer (Maxim) regarding errors in the datasheet of an ADC. It is certainly not a common enough occurrence that I would waste my time retesting every component I use.
Yea, I guess I have just been on this blue sphere long enough to see some strange things that I have learned to not trust anything.
I have a solid state relay on my current board design that uses an internal LED in the part to drive the output section.
Before I send out 600 of these to be populated I’m going to bread-board a couple of the parts in the actual circuit. And I have already read the datasheet and done the math for the current limiting resistor.
And, yes, I will do a small proto run of about 15, and increment that by a factor in a second run, before I do the full run of 600.
It will be about $10K coming out of MY pocket, and I can’t afford stupid mistakes.
Yes, like those wonky electrons.
And that is just fine if that is the process you want to follow. The op is not risking $10K on 600 boards so his process is likely to be different. Don’t berate him because he’s not following yours.
It’s not exactly a SSR if it does not already include a current limiting resistor.
Yes, they’ve mastered the art of controlling the longevity of their products, probably by using 90 degree corners.
There is a degree of truth to that and unfortunately the upgrade cycle is much shorter for some products. Often it is not because the consumer “wants” to upgrade but because many of today’s products are less expensive than the cost to repair them or, in some cases, to refill their consumables. For instance many ink jet printers can be purchased for less than the cost of purchasing new ink cartridges.
[quote]The CPC1017N is a miniature single-pole,
normally-open (1-Form-A) solid state relay in a
4-pin SOP package…[/quote]
now it’s wonky datasheets…
Thank you for posting that datasheet. You are correct in the sense that the manufacturer calls that an SSR. To me that’s just an opto-coupler with FET outputs. The definition of an SSR that I am familiar with is.
Solid State Relays are normally-open semiconductor equivalents of the electromechanical relay that can be used to control electrical loads without the use of moving parts.
Perhaps I take the word “equivalents” too literally?
[quote=“1.21Gigawatts, post:97, topic:6507”]
Yes, they’ve mastered the art of controlling the longevity of their products, probably by using 90 degree corners.
[/quote]In mass market commodity products the cost of returns/warranty and the cost of manufacture is highly correlated. If spending one more penny doubles the life it doesn’t get spent if it isn’t offset by reduced return costs.
I mentioned off shoring in my original for a reason. I don’t know that this applies across other disciplines of course.
http://www.gadgetsnow.com/jobs/95-engineers-in-india-unfit-for-software-development-jobs-claims-report/articleshow/58278224.cms
This is the basis for my argument that pulling some random board and using it as a model of acceptable practice might not be wise. But, best practices evolve because they are questioned. Do you want to develop habits that work on one circuit but might fail on another?
An engineer from Packard Electric told me they got in a spanking new expensive control system that would fail periodically. After weeks of engineers on site to diagnose the problem they tracked it down to the fact they never tested it with the cover on. It took adding a single pico farad capacitor to compensate for the effect. Sometimes small things don’t matter. Sometimes they do.
Here is the latest version of the schematic.
A few questions:
I added PWM based control for the fan speed. I chose a transistor (TIP50TU-ND) capable of handling 1A (need ~ .2) and has a switching freq of 10MHz. I think this is well within the spec, may be overkill?
Temp monitoring would be great but from what I have read that requires a DA converter for the Pi. Not sure if I want to go there right now? I just want to be able to tune fan speed if it is annoying.
I ordered some LEDs and will play with resistors to get the brightness right. Not really a big deal as this will mainly be for testing/troubleshooting.
I’ve also got a few free GPIO connections that I was thinking of terminating to connectors in case I need to monitor something in the future. Does anyone see this as a bad idea?
Should I leave some pads/holes anywhere to add any components if needed?
Thanks
Adamsaw-V5.pdf (91.0 KB)
Okay, I’ll try to help.
Is this for the case fans?
And this is why I recommended Spice. I suspect that that transistor will not fully turn on with a logic level signal.
I’d suggest you try a different part. I’d look for a N-FET package that will operate with a logic level input.
Your drawing is still lacking the flyback diodes across the relay coils.
D1 appears unnecessary.
D2, the other D1… Does KiCad even see that as a vaild RefDes? D2 is rated for 5A, however you have 7A fused. Now, at first glance that seems not unreasonable. However, each one of the DRV8825s can provide as much as 2.0+A (depending upon heat sink) per EACH coil (2 coils per stepper).
That could mean 8A just for the steppers; which will let the smoke out of D2.
And, I’m confused what you are doing with the optocoupler. Take a look here:
That should get you started.
Thanks Jim,
I appreciate the feedback and help and I address your points below.
Your drawing is still lacking the flyback diodes across the relay coils.
As far as I undertsand the UNL2803 has an internal flyback diode. This is why I removed the previous diodes.
I’d suggest you try a different part. I’d look for a N-FET package that will operate with a logic level input.
Will do.
D1 appears unnecessary.
ok. Thanks
D2, the other D1… Does KiCad even see that as a vaild RefDes? D2 is rated for 5A, however you have 7A fused.
The D_Schottky_1. Thanks I need to update this. The Schottky below is rated at 60V and 10A max. http://www.mouser.com/ProductDetail/ON-Semiconductor/MBR1060G/?qs=sGAEpiMZZMtQ8nqTKtFS%2FCKUxMvjsmGzZVi%2b%2budIBp0%3D
Reference changed to D2.
each one of the DRV8825s can provide as much as 2.0+A (depending upon heat sink) per EACH coil (2 coils per stepper).
Thanks. I added the 3rd stepper headers in recently and did not update the power input.
I downloaded a copy of spice (LTSpice XVII) and will try and get up to speed on this shortly. I also see some comments showing some spice integration with KiCAD? Is this possible to run simulations from KiCAD or do most people draw circuits in Spice and run in that environment?
And, I’m confused what you are doing with the optocoupler. Take a look here:
Thanks. I see the ground was not connected to the cathode (+5V instead) on the output side of the optocoupler
Hi Jim. I see this can handle 60V and 30A and be controlled by a microcontroller. A question. In my application, are the relays preferred to switch the loads because they provide better circuit isolation?
D1 appears unnecessary.
Is D1 not required because the inductance of the fans is so small?
Also is it good practice to pull the gate of the transistor to 0V with a high resistance ground connection?