Transistor Selection for Switching Relay Coil-with a little bit of info on my "ARSC"

[mackrackit]

So I take it your punch presses don't have a massive flywheel like a small manual punch (the kind I have more experience operating)? Are these massive industrial punches or smaller interchangable die style punches?

These were built to replace the massive flywheel manually operated types. They are more along the lines of the smaller type but the dies are a custom build.

Picture a 6 inch cylinder driven by a two stage pump on a 15 hp electric motor. That pushes the punch. The other one has two 4 inch cylinders in parallel driven the same way.

One is designed to punch a set of holes through a 1/4 x 6 x 6 inch piece. The other will take two pieces of 1/4 x 2 x 2 angle and punch a set of holes along with shearing the ends at 45 degrees on one step.

The plate punch has a feeder that uses an air cylinder to push the part into place from a stack. The angle punch uses a hydraulic cylinder to feed the parts.

Both machines have sensors, (pressure, mechanical, IR ) to control the operation and check for mechanical errors, like a stuck part or no parts.

Sorry to jump off topic, but this is an area that really interests me...

It is your thread

[rxforspeed]

These were built to replace the massive flywheel manually operated types. They are more along the lines of the smaller type but the dies are a custom build.

Picture a 6 inch cylinder driven by a two stage pump on a 15 hp electric motor. That pushes the punch. The other one has two 4 inch cylinders in parallel driven the same way.

One is designed to punch a set of holes through a 1/4 x 6 x 6 inch piece. The other will take two pieces of 1/4 x 2 x 2 angle and punch a set of holes along with shearing the ends at 45 degrees on one step.

The plate punch has a feeder that uses an air cylinder to push the part into place from a stack. The angle punch uses a hydraulic cylinder to feed the parts.

Both machines have sensors, (pressure, mechanical, IR ) to control the operation and check for mechanical errors, like a stuck part or no parts.

It is your thread

Wow-those sound a lot more advanced than any of the basic fab shop equipment I've operated before-presses, slip rolls, shears, etc. I've got years of experience working in fab shops, welding and fabrication, and various other contract fab work (such as building smaller industrial cleaning tools and equipment), but most of the punches I've ran were actually quite dangerous-they were all manual and nothing was electrical except for the 240/480VAC motors that powered up the flywheels. No sensors, pneumatic loaders, hydraulic ejectors, etc.-just one person trying to keep from losing a finger or a hand while holding what could sometimes be a quite large and heavy plate while at the same time trying to keep it centered in the punch. I'm sure quite a few shops have more sophisticated equipment like yours, but the places I had worked for were just getting CNC press and leaf brakes just a couple of years ago.

Since I've gotten into electronics, I've found so many possible uses for MCUs and potential products that could be built and marketed rather inexpensively on a smaller scale. These things are used in toothbrushes, toys, industrial and medical equipment; every USB programmer I've seen has an 18F2550-the possibilities are limitless. Every day we're making even greater technological advancements and improvements, so I figured I was way past due to check out what this field had to offer, and I'm glad I did. I enjoy working with electronics more than I do anything else, which is the number one reason I'm going back to school for a bachelor's in Electronic engineering. My ultimate goal is to have my own business, whether it's manufacturing products on a small to medium scale or contract work involving programming and creating software for bigger corporations. The demand for programmers and software creators for custom applications grows constantly, almost daily at an astonishing rate. To be honest, it's pretty scary thinking about what our children's and/or grandchilden's career options will be-even before the next century. I believe, possibly within our own lifetimes, pretty much every job and or career that humans take for granted today could very well be replaced with an automated system or robotic application-given the time and the rate of growth and expansion of the technology...

Think about it-in most situations in "war", combat, or possible hostile territories, we have un-manned aircraft and robotic surveyers. That's actually great for saving the lives of our brave soldiers, but that technology is being adapted into more than just our armed forces. A great deal of jobs have been lost in many industries (especially the automotive industry) within the past ten to twenty years due to automated robotic systems-assembly line part/component installers, welding robots, automated automotive painting robots, etc. The list continues to grow and more people are laid off and unemployed because their work has been completely automated by machines. Instead of corporations paying hourly, weekly, or yearly wages or salaries to human workers, they invest a single or few workers yearly salaries or wages into the construction of an automated robotic system that doesn't need to be paid, needs no breaks or sleep, never complains or goes on "strike", only really needs minor periodic maintenance, makes WAY less errors or mistakes (if any at all) than the human worker(s) it's replaced, etc. It really scares me to think how that technology will be carried over into mid-sized or even small businesses/corporations in the next few decades. Are you paranoid that some jerk-off at Mickey D's might cough or spit (or possibly something even worse) in your order-especially if you have to send it back because of a mistake on their part? Imagine walking into your local fast food joint, pushing a few buttons on screen at the counter to place your order and receiving it exactly as ordered, prepared by an automated robotic system without any human workers present to touch your food. It's very possible that could happen in a matter of just a few years...

Well, I've jumped pretty far off topic (both of the previous ones mentioned in the last few posts) and I'm up WAY past my bedtime, so I think I'll start a new topic in the "Other" section of the forum to attempt to discuss some of these possibilities with others when I get a chance tomorrow. I'd really like to see how others view this dilemma. The more our technology advances, the more likely systems like these are going to continue to drop in price and become more available and attractive to not only large manufacturers and corporations, but small and medium-sized businesses as well. Sooner or later, I sincerely believe that any and all jobs that were once handled by people will be fully automated and handled by machines or robotics, at least in some form. I just hope it doesn't affect my 8-year-old son by the time he graduates high school in a little over nine years, and hopefully his graduation from college four or more years after that (I won't MAKE him go right after high school, but I've tried my best to get him to work on programming these PIC MCUs, building some smaller "spy gadget"-style circuits, and electronics in general; hell, I've even paid him $4USD/hour to mostly watch and "help" me assemble a few circuits here and there, which is a great rate for a kid who's not even old enough to work yet, but he'd still rather play ball and skateboard with his little "skateboard punk" friends than become a "geek" like I have in the past year or so)...

If any of you guys/gals would like to share your opinions/thoughts/concerns about that topic, just look for a new thread in the "Other" section of this forum-hopefully sometime tomorrow...

In the meantime, I'll go ahead and order the parts that Melanie had suggested and I'll post any other questions, comments, concerns, or additional cries for help here after I receive those. I think I've got the hardware aspect of the "A.R.S.C." project figured out now, but I'm sure I'll have a few questions about certain code snippets that I'll post under the "Code Examples" section when I get to that point.

Again, thanks for your time, help, cooperation, and patience with me while I build this project. Any and all input is greatly appreciated, so please don't hesitate to correct me, criticize me, help me, or just straighten me out in the event I've forgotten an important or critical part/component/or anything else that would be a major mistake or cause a malfunction with this prototype. I truly appreciate the help, direction, guidance, and input you all have given me so far-I promise you it's not in vain. I've already learned quite a bit from this forum and I hope to continue to learn as much as I possibly can through the knowledge and wisdom of people like you, Dave and Melanie. I greatly appreciate the information you've shared with me so far...

Thriving for more knowledge,
-Adam Collins

[Melanie]

You won't need Diodes across the Relays, or any other components with the ULN2004 - they're all built-in to the chip, which makes it neat and easy to connect. Download the Datasheet for the chip. The pin with all the Diodes internally connected to it is wired to +12v. +12 also goes to one side of your Relay. The other side connects to one of the seven Output channels. The input to the channel connects to the PIC I/O. Drive High for Relay ON, and Low for Relay OFF. Unused channels can simply be left unconnected. Good practice states you ground the unused inputs, but you don't have to on this part.

There's nothing wrong with putting Relays on your 5v line if your 5v PSU is solidly built (and it looks like Dave builds solid gear!). Most folks on this list are hobbyists or new to electronics. The chances of building a crappy supply are high, putting a heavy load (Power Relay Coil) onto the same voltage line that becomes a REFERENCE for your ADC or Comparators is asking for trouble at best, and at worst is going to start resetting your PIC by tripping it's MCLR or corrupting EEPROM.

[rxforspeed]

You won't need Diodes across the Relays, or any other components with the ULN2004 - they're all built-in to the chip, which makes it neat and easy to connect. Download the Datasheet for the chip. The pin with all the Diodes internally connected to it is wired to +12v. +12 also goes to one side of your Relay. The other side connects to one of the seven Output channels. The input to the channel connects to the PIC I/O. Drive High for Relay ON, and Low for Relay OFF. Unused channels can simply be left unconnected. Good practice states you ground the unused inputs, but you don't have to on this part.

There's nothing wrong with putting Relays on your 5v line if your 5v PSU is solidly built (and it looks like Dave builds solid gear!). Most folks on this list are hobbyists or new to electronics. The chances of building a crappy supply are high, putting a heavy load (Power Relay Coil) onto the same voltage line that becomes a REFERENCE for your ADC or Comparators is asking for trouble at best, and at worst is going to start resetting your PIC by tripping it's MCLR or corrupting EEPROM.

I will download the datasheet for the ULN2004 in the next few minutes, before I place my order for these parts. As for the power supply, could I get by with installing an additional 5V regulator (7805, LM2931T-5.0, LM2940CT-5.0, etc) to power a seperate 5V rail for the 5V relays that would be pretty much isolated from the PIC's 5V supply?

Don't get me wrong, I'm going to take your advice and install the 12V relays on this prototype, but I've got a lot of the 5V versions of the relays and figured that if the additional regulator would allow me a "clean and solid" power supply, then I could go that route for the next project I build using the 5V relays.

I usually always install both a 10uF (50/63V electrolytic) and a 0.1uF (200V ceramic) input cap on the inlet side of the regulator (and in this case, from +12V to ground), as well as the same type and value capacitors on the output side of the regulator as bypass caps. Is this sufficient for a solid power supply; it will be connected to the vehicle's ignition hot or to a constant hot fused position by means of a SPST switch so it only operates when the owner wants it to. I know that sometimes the alternator can cause voltage spikes and current surges throught some components, so I really plan on getting my hands on some good automotive 5V regulators like the LM2931T-5.0 (only 500mA in a T0-220 package) or the LM2940CT-5.0 (1-1.5A in a T0-220 package), which both have built-in protection designed for these types of spikes and surges...

[Melanie]

That's fine. Your isolating the PICs supply from that used for other significant switching loads, which is the whole idea. What that 'other' supply becomes, is irrelevant.

I really can't comment on the size of your Capacitors without knowing what your total worst-case load will be and what is actually going to be used as the Regulator. Build it and see...

If it's an automotive application, you should really be using 12v Relays. All you are accomplishing (other than using up your stock of 5v components) is heating up the planet! When the ice caps melt, it's now public knowledge that it'll be YOUR fault.

[rxforspeed]

That's fine. Your isolating the PICs supply from that used for other significant switching loads, which is the whole idea. What that 'other' supply becomes, is irrelevant.

I really can't comment on the size of your Capacitors without knowing what your total worst-case load will be and what is actually going to be used as the Regulator. Build it and see...

If it's an automotive application, you should really be using 12v Relays. All you are accomplishing (other than using up your stock of 5v components) is heating up the planet! When the ice caps melt, it's now public knowledge that it'll be YOUR fault.

I'm sure the "carbon footprint" of my modified vehicles doesn't exactly qualify me as an "environmentalist", either.

As for your suggested components, I have downloaded the datasheet for the ULN2004 and briefly read through it. Since I'm currently classified as a "student" (even though my classes don't begin until January), I've requested some samples of both the ULN2004 and the ULN2803 from TI, but at least ten of each are on my next Digikey purchase, which will be placed before the end of this weekend. The 12V relays are coming from both Digikey (two different kinds-Omron's G5LA series and Tyco's PB114012-eight of each for the time being) and anykits.com (along with a few additional PIC peripheral components and development boards). I should have both orders in by the 6th, so I'll concentrate on writing the code for the '690 in the meantime...

I made sure to download the correct manufacturer's datasheet for both transistor arrays...

Again, I really appreciate the time you've taken to help me out with this. It's people like you (Melanie and Dave) that make this forum a wonderfully educational site that I'm proud to be a part of. Thanks to you guys, I'm sure that my "A.R.S.C." project will be a success...

Sincerely,
-Adam Collins

[RussMartin]

My personal choice, at the tinkering stage, would be to use a plain old 2N7000 MOSFET to drive each relay (with flywheel diode, of course).

Multiple device drivers are handy and certainly have their place, but they also have some inherent limitations, one of which is the total power dissipation available in the DIP package. For example, see the thermal curves for the ULN2004.