Merging Current and Voltage Sources - How Can I Do This?

Well I'm sure someone will correct me if I'm wrong but won't you need 620ma @5v and increase the voltage then to 12v....

No, I need a +12V output with 300mA current on the positive terminal of the pumps motor and -12V output with 300mA on the negative terminal of the motor. I can't seem to design a circuit that will achieve this using the NI USB 6009. Any help would be appreciated

So your 5V power source had the Amperage needed to drive the 300mA at elevated voltage?

You can not get out more than there goes in. Its some stupid law that is often overlooked when one wants something desperately but does not know how to.

Limited to 5V and 5 mA..... Says it all. Maybe you can get rid of the limitation.....

Nope I don't see this to work. Nice schematics though.

Here's the datasheet of the DAQ in question

http://www.ni.com/datasheet/pdf/en/ds-218

The motor on the other hand, +/-12V 300mA power? Are you sure it's not 12V or 24V DC 300mA? Can you provide a manufacturer and or part number for it?

Simply put if the motor is a simple on/off single speed type then build a separate +/- 12V (?) power supply and switch it using the DAQ digital output driving a separate 5V logic in to high current 12V logic out switch. Think transistor circuit with gate being driven by DAQ output.

Its a little more complicated if the motor is variable speed but again a transistor circuit should do the trick, although pulse width modulated control is preferred however this can be implemented in Labview. Others may post some circuits but we really need to confirm what motor you are trying to control. It would actually help if we knew what the motor is doing and its load-what it is turning (this can actually effect the control circuitry, especially if precision speed and torque control are required).

Regardless you need a separate power supply to provide the +/-12V 300mA and a separate circuit to interface the 5V logic control signal from the DAQ to drive the motor.

This is the pump in question: https://www.adafruit.com/products/1150

Will this work ok?

The motor is a simple 12V DC, up to 300mA pump motor (depending on what you are pumping). If your pumping air the load current will be much less.

You need a 12V DC (+12V / 0V) supply not a 24VDC (+12V / -12V supply). That simplifies things.

The circuits you have posted so far won't work for various reasons. Someone should hopefully post a simple transistor circuit that will do the job for you soon (basically a 5V logic controlling a 12V 300mA DC load using a transistor or similar circuit).

ok so this is a 12v motor 200-300mA current requirement...they list an excellent chip for this application L293D that has 5v control with any number of switching requirements....

http://www.adafruit.com/product/807

....and find a power supply here for example...

http://homemadecircuitsandschematics.blogspot.com/2013/02/how-to-make-simple-220v-transformerless.html

Increasing the supply voltage to 12V is a step in the right direction.

I would suggest you also install an OP-Amp output feedback circuit to control the gain for testing purposes.

G = Rfb/Rin

A variable resistor (potentiometer) works best.

Remember that the inputs to an OP-Amp must equalize in order to stabilize output.

I missed these two circuit variations earlier. While the use of a larger supply will make it possible for the zener to work, neither of these circuit will work in a controlled fashion. In the first the zener will not get enough current to flow though it to achieve the zener voltage. In the second circuit the current will be too large and quickly detonate the diode. Then there is problems with Q1. This transistor (2N3904) has a collector current absolute maximum of 200 mA. Then there is the collection of resistors attached to the emitter of this transistor.

This is so far away from working that...

No.

GA

Although I don't see where you have stated such, it would appear that you wish this pump to be able to run in both directions. Being a peristaltic pump and able to be reversed, that will be OK, but it makes the circuitry a bit more complex.

You are showing separate circuits for each direction whereas in reality they must be combined, ie. you must reverse the Vcc and Gnd connections to the motor without creating a short circuit in the process.

You also don't show (in your latest iterations) the input from the DAQ, so I have no idea where you intend to get your signals from.

Below is a typical DC motor reversing circuit that may give you some ideas, it has separate inputs for both directions, and you would have to link those to your DAQ (possibly via an open collector buffer. I have no knowledge of the DAQ output possibilities, you would need at least 3 - off, forward and reverse.

You can likely get a dedicated driver chip that does it all.

Exactly!

A 12VDC 300mA motor, is a motor that, when given 12 Volts of DC power, will draw, at most, 300 miliamps of current. (As long as there are no flaws or short circuits, but rated values assume that the circuits are set up correctly, and that the components are within manufacturer specifications.

To scall93, I would like to say: First off, welcome to CR4, you'll find a lot of helpful people here. Secondly, I would recommend that, before you go any further, you review the theories of constant voltage sorces and constant current sources. Constant current sources are used only in places where they are absolutely required. Constant voltage sources are used everywhere, from the battery in your flashlight or cell phone all the way to the power grids of nations. Think of it, this way, Voltages are the electrical 'pressures' of the energy, so each branch in the circuit should be rated to handle the 'pressure' the power supply is putting out. The current is the 'currency,' each branch will 'draw' a certain amount of miliamps, and the power supply has only so many milliamps it can give out. It's okay if you 'underspend' and 'leave some miliamps in the power supply,' but if you try to 'overdraw your miliamp account,' then Bad Things happen, the power supply 'gets weak,' and the voltage starts to drop, the power supply could be damaged, and the branch circuits may also get damaged from the 'undervoltage' condition they are suffering through.

[I may not make sense here due to desired embibements that have been successfully achieved. So please bear with me. ]

None of the magnificent circuits you've provided here are complete. None of them include the load you wish to drive. I suspect that once you include the load in these circuits you will see much more clearly what you want to do and how to achieve it. I'm not sure if combining these signals will be best done by a diode OR circuit, providing one circuit on the positive side of the load with the other (possibly inverted) on the negative side or if a summing amplifier circuit is needed prior to a current buffer.

Pleasant dreams.

Reality and probably Tylenol will come in the morning.

I'm confused by that first circuit (haven't even looked at the others) - you say the output from the DAQ is limited to 5v@5mA - yet you show an output of 5v@300mA from your circuit without any obvious other power source....How did you do that?

I would suggest that a bit of reading up on open collector buffers may assist you.

Here is a link that illustrates several OP-Amp motor control designs that should help.

https://www.google.com/search?q=operational+amplifier+motor+control&biw=1920&bih=993&tbm=isch&imgil=d22YkMuIMBIVZM%253A%253BJvzc8Kyy5xGwrM%253Bhttp%25253A%25252F%25252Felectronics.stackexchange.com%25252Fquestions%25252F68109%25252Fop-amp-vs-direct-control&source=iu&pf=m&fir=d22YkMuIMBIVZM%253A%252CJvzc8Kyy5xGwrM%252C_&usg=__rMfBgGEmboZFgmZ1oKo0tlTjS5E%3D&ved=0CCcQyjc&ei=2yLvVK7uF7X9sAT60oH4Ag#imgdii=_&imgrc=d22YkMuIMBIVZM%253A%3BJvzc8Kyy5xGwrM%3Bhttp%253A%252F%252Fi.stack.imgur.com%252FvQDYK.png%3Bhttp%253A%252F%252Felectronics.stackexchange.com%252Fquestions%252F68109%252Fop-amp-vs-direct-control%3B600%3B493

If you want to feed your motor with a bipolar voltage (+/- 12) AND you want to limit the current with circuit #1 (which is a current limiter, unipolar), get a rectifier bridge and install it with the AC terminals is series with your motor. Put circuit#1 across the DC terminals of the bridge (with the correct orientation). That way, circuit#1 can limit the current and circuit #2 can reverse the direction.

Ok, a cup of coffee in me and no need for any Tylenol. So far the morning is going well. Now onto trying to be helpful here.

I still believe that adding the anticipated load device to any schematic will help solve many misunderstandings and there are certainly many misunderstandings in these two or three schematics.

Your first schematic, assuming the load is supposed to be connected between flag marked "5V,-300mA Outp" and the common return you do not have a current source at all at that node. That node is driven by V1, a voltage source. The entire rest of the circuit is nothing but an additional load for V1. This is good because this circuit is doing nothing. It resembles a current source circuit but it is actually doing nothing. The nominal zener voltage for a 1N4733A is 5.1V. This diode is not clamping anything.

Your second schematic of two TL081 operational amplifiers has absolutely no feed back circuitry which cause these amplifiers to work purely as comparators. They will try to turn fully ON to one rail voltage or the other depending on the voltages at the inputs. The TL081 is a very low output power device that can only drive a few milli-amperes of current. This is implied but not out right stated in figure 9 and 10 of the data sheet I linked to. These op-amps cannot provide enough power to drive directly 300 mA. Also a motor is an inductive device. It will generate a back EMF and revese current flows that must be handled in the circuit design.

Additionally your description of a +/- 12V DC pump makes no sense to me. A bipolar DC motor is reversible. Few pumps are reversible and many that shouldn't be reversed will be damaged by trying to.

Your first schematic, assuming the load is supposed to be connected between flag marked "5V,-300mA Outp" and the common return you do not have a current source at all at that node.
Correct, his load should inserted between the positive supply and the flag (the transistor collector). The transistor collector should not be connected to the positive supply.

Do you need to adjust the speed of the pump?

If not, then the circuit can be quite simple. You'll need a power supply that converts mains voltage to 12 volts DC. This one's in a neat package and relatively cheap:

http://www.digikey.com/product-detail/en/VSK-S5-12UA-T/102-2666-ND/3881238

Then you can simply use a transistor to switch the 12 volts to the motor. The transistor must be rated to handle the current and voltage and you must put a reverse current protection diode across it. There are also relays that will activate with 5 volts at under 5mA.

If you need to adjust the speed of the motor, then the circuit will be more complex. Search for 'PWM motor control'. There are lots of examples out there as well as complete modules to do this.

It sounds like you still have a lot to learn. Keep reading. Keep looking.

Sage advice....

I'd bung the 5mA into the base of a 2N3055, tie the emitter to the 0V rail, lob a suppressed electromechanical relay in the collector, and switch a separate 12V supply with it onto the motor. Then, I'm funny that way.

Skip the relay - tie the motor as the load. Single transistor solution (add a free wheeling diode around the motor to be kind - but you ill probably get away without it.)

It's still a little unclear, do you want the pump to be able to be driven in both directions?

It's clear to me the OP doesn't understand how to read a component specification sheet.

Hence the need for us to not get too carried away with our answers and possible (but perhaps not applicable) solutions and baffle the poor fellow.

The GA is for the optocoupler solution. Easy and reliable.

Simple solution... h-bridge package L298.

Have you taken into account the starting current of the motor you are using. It can be several times the normal running current. Depends upon the motor designer....the load etc..

As someone here has already mentioned, why bother to restrict the current? Putting say a 1 amp fuse in the circuit, assuming the starting current to be less than that, is as good a method as any.....

Controlling a voltage and a current together, is rarely needed and adds a complication that is simply not needed here.....especially for a beginner trying to design something. Making the whole operation far simpler when not needed.

Remember also, you need to snub any high back EMFs carefully, or they will damage your circuit AT THE FIRST SWITCH OFF!!!

I was unable to decide if you needed fwd and rev or not. You need to make a statement on that point!! It changes the design quite dramatically......and the back emf design as well.....

Hate to be negative but how can you design these circuits with so little understanding of basic electricity?

I just re-read the original post, and you're trying to drive a pump with a data acquisition unit?

A Data Acquisition Unit is a Meter, it is designed to read values and record them, not supply power to run equipment.

You need to have some current-interrupting device between the power supply for the pump and the pump itself, with the device taking its orders from the 'go/no-go' signal from the DAU.

I strongly suggest that you get the company electrician or electrical engineer to help you, they will better be able to put 'eyes on the problem,' and find the solution needed.

I noticed the data acquisition absurdity early on and forgot to mention this. scall93 is either so far over his head or playing us all for fools.

This thread reminds me of a conversation I had about absurd CR4 anonymous poster questions. It started off something like this:

AP1: CR4 gurus I need your help. My 1962 Cavalier has a flat tire and makes a weird sound when I try to use it. I looked at some of your helpful "caption this" images and wanted to know if I could use a fork to fix my car.

Guru1: Just put it on Craigslist

Guru2: A fork is fine for spaghetti

Guru3: I'd just burn the tire.

Guru2: In all seriousness lifting a car with a forklift is a common but dangerous practice. You have to know where to set the tines.

AP2: Tyne Daly is a very good actress.

Guru4: Did you try Google?

AP1: No, I have a tuning fork. How do I get this to turn the tire lug nuts?

Guru5: Global warming is a myth.

"I noticed the data acquisition absurdity early on and forgot to mention this. scall93 is either so far over his head or playing us all for fools."

My vote is for 'in WAY over his head,' since people who are trying to "leave us punk'd" in the modern vernacular (or "make us look over our shoulder for Alan Funt" for those old enough to get the reference) tend to do it annonymously(1), since having a history of trolling the board tends to leave you with a bad reputation, and gets you either snarky answers to even your serious questions, or gets you a 'face to face' meeting with Mr. Banhammer.

That one guy, AP#1, seems to get away with a lot of 'stupid questions,' seems like every time he opens a thread it's something to drain the collective IQ from the room. Good thing AP#2 and AP#3 tend to show up quickly to 'politely' (in the Greater Internet Flipwad(2) Theory manner) show AP#1 the error of his ways(3).

Notes:

1) Yes it's misspelled, no, I'm not going to fire up the clunky in-forum ap to fix it.

2) You know what that word really is, I don't need to spell it out for you.

3) They also generally make 'other comments' about AP#1 and his ancestry, but I'm staying out of that mess.

Is it warm in here or is it just me?

Has someone burnt it down AGAIN?

Globe al warming.....

LOL!!!!!

I'll agree, just sounds like he's in way over his head. He sounds like one of the students that I recently mentored in a senior design project. It was a group of 5 Mech E students. We'd provided a small amount of funding for parts and outside labor (machine shop, etc). The students were to do all of the mechanical design, but they were short on EE and programming skills. I dare say, they all learned a little EE by the time I got through with them.

I was a little disappointed with the school. A project like that should have been interdisciplinary. There are so few jobs where only a Mech E is necessary. Most projects are teams with various engineering disciplines involved. I'd much rather have seen the project 'staffed' with students from EE, Com Sci, Chem E or whichever as needed.

On the other hand, I've seen plenty of non-EE's that could handle a good bit of EE. They actually understood Ohm's law, etc. I suppose the lucky team had one of those.

Down here the first year of an Engineering course covers EE, ME, Comms, Micros, Power, etc. Gives the students at least the basics and also gives them a chance to see what fields they liked. Quite interesting that when I was there more people who were planning on going EE changed to ME after the first year than the other way round.

Joke/sage advice: How do you gauge a newly graduated Engineering student?

Ask them how they would solve a simple practical hypothetical problem, if the first thing they say is "I would model it", they need practical experience because it doesn't look like the University gave them any.

That's excellent that they cover a wide range of fields. One is so much more valuable with at least a basic knowledge of a variety of fields.

When I was in school, EE was the big field with more than twice the number of students than ME. This was at the time (mid 1980's) when PC's were just getting going and there was plenty of interest. I took my son to my alma mater for the nickle tour when he was looking at schools in 2010. By far easily 3 or 4 times the number of students were interested in ME vs. EE. EE no longer rules.

I wonder why that is, the maths is the same for both after all.

The gap's probably going to get wider with the new specialty courses like mechatronics, specialty computer sciences (AI, etc), robotics and renewable energy.

Is this the new 'cool' thing to go into? Are we looking at another shortage of EE's, again. Heck, we the few cannot be expected to do everything (else) you know.

"Are we looking at another shortage of EE's, again."

Do you mean a REAL shortage, or yet another 'claimed' shortage by companies who want to bring low-pay Engineers over on H1B Visas.

Then again, when the companies look for the cheapest engineer they can find, they usually get what they pay for. *cough*Loke*cough*shloki*cough*

The only real shortage is experienced and motivated EEs and MEs.

Universities are churning them out like anything every year but many lack the motivation and ability to upskill and teach themselves to handle the ever changing environment real career life thrusts at them......

*cough*Loke*cough*shloki*cough*

Scall93, did any of this above help or have we confused you with too many options (some slightly contradictory)?

We would love to hear back from you !

Why not use the relay outputs from the DAC to switch open and closed some physical relays (definite purpose contactors), to apply the power to the motor coils forward direction sense, and then reverse sense when needed, just by using contactors that are physical relays, much less likely to fail and burn up.

Shirley the DAC has more than one logical output? yes? no? maybe? Thus when no output is required to the motor, then both outputs are at 0 volts, and the relay that was active goes open circuit.

It appears from another very similar thread posted anonymously that this is part of a larger university project......

I am building a processing for a university project and am looking for some recommendations of components that will work well with the NI USB-6009. This DAQ is limited to 5VDC output @5mA.

http://cr4.globalspec.com/thread/99698/Recommend-Components-for-Miniature-Processing-Plant-that-will-be-Automated-using