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| Beginner Components? |
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| JacobEdward:
--- Quote from: WattsUp on February 22, 2015, 09:09:12 pm ---Something you should definitely look at are 555 timer circuits. If you understand the basics, you will be amazed at what you can do with them. http://www.waitingforfriday.com/index.php/4-Bit_Computer --- End quote --- I've looked into 555 timers before and found this website http://www.555-timer-circuits.com/, do you know anything that might give some basic circuit tutorials for beginners? Also, just to be clear, a 555 isn't absolutely necessary when you have a microcontroller, but it would be something to use if a whole microcontroller wasn't necessary? |
| JacobEdward:
--- Quote from: Simon on February 22, 2015, 09:33:59 pm ---Completely confused there, what micro controller are you using and what are you trying to achieve ? --- End quote --- I'm a convert from the world of Javascript so I'm using an Espruino microcontroller, the cost of using a language I already know how to program in is that it's substantially slower than typical microcontrollers, but intuitively it seems like there would be a simple work around for this... turn an external component on that will have a PWM of 50MHtz until you tell it to turn off... the reason why this might be necessary is that you would need a higher frequency and voltage in order to control the speed of AC motors... As far as the op amp, I was referring to controlling a DC motor that requires more current than the microcontroller puts out... |
| WattsUp:
Yes, a microcontroller could do what a 555 timer does, but it is cheaper, simpler and more fun! I will try and answer your previous question from what I understand. Firstly, I think you misunderstand what an op amp does: it amplifies a signal (among other functions). It can't source more current, and you have to feed it a higher voltage than the maximum level of the amplified signal. Secondly, you can make a H bridge I believe, but be careful when working with high currents (keep it fused) and make sure you have the right transistors. Tbh, a pre made IC will only cost you £2 at most though. Motors are not my area of expertise, but I don't think you fully understand how to control one and how your micro controls them. Google around for pre made designs, and build on those for your own requirements. What Simon is saying is that you are not clear with what you are trying to say. Maybe if you ask the question again in a more detailed manner we will be able to help you out a little bit. Ben |
| JacobEdward:
--- Quote from: WattsUp on February 22, 2015, 09:45:46 pm ---Firstly, I think you misunderstand what an op amp does: it amplifies a signal (among other functions). It can't source more current, and you have to feed it a higher voltage than the maximum level of the amplified signal. --- End quote --- When you say amplifies a signal, what you mean to say is voltage is being added to an output that can still be controlled by the input signal that has a substantially lower voltage (aka if a microcontroller outputs 4.7 V to a OpAmp that amplifies the signal to 12V, the microcontroller can still turn off the 12V by turning off the input to the Op Amp). I was under the impression that if you add Voltage to a signal, you are also adding current, all you have to do is increase the resistance (or wait... reduce the resistance? lol I still need to empirically prove ohms law, I should do that today actually) and you will find the increase in current you're looking for... no? --- Quote from: WattsUp on February 22, 2015, 09:45:46 pm ---Maybe if you ask the question again in a more detailed manner we will be able to help you out a little bit. --- End quote --- My question about increasing the frequency was in reference to controlling AC motors with a microcontroller... when googling around, I found this http://en.wikipedia.org/wiki/Variable-frequency_drive and these things cost hundreds of dollars, but the fundamental thing they're manipulating is the frequency and Voltage applied to the load... right? My microcontroller has the ability to change the frequency it is capable of outputting, it's just severely limited because of the extra work it does in order to be programmable in Javascript... the question I was asking is why wouldn't it be possible to connect my microcontroller to a second chip that was also capable of outputting 72MHtz (but didn't have the extra Javascript work) and completely overcome this limitation... those chips are about $5 each, and with relays or whatever else, why couldn't that then be just as good of a solution to controlling the frequency than this other thing that costs hundreds of dollars... |
| Simon:
JavaScript does not exactly sound like a microcontroller language. I don't know what JavaScript entails as I barely understand C myself however I'm pretty sure you could do some stuff in C. The other thing I think you are missing is that any microcontroller will produce a square wave output where as usually you are controlling a motor with a sine wave. What is usually done is to approximate the sine wave with a varying duty square wave so that the average voltage of the PWM output represents the average sine wave voltages that you would otherwise supply the motor. This is why your variable frequency drives are not cheap, they are not necessarily simple. The other thing is if you are using the PWM capability of your microcontroller once this is set up through whichever language you choose it should run very efficiently as it is a separate hardware peripheral on the microcontroller chip so I'm not sure how the programming language is affecting its top frequency. A bloated programming language may mean that it takes you longer to alter the PWM duty but the frequency should be achievable. An operational amplifier or carry out any amount of operations as the name suggests on an analogue signal. You can use it to multiply or divide a signal or add signals together. Obviously the operational amplifier needs a power supply, the input impedance of an operational amplifier is theoretically infinite in reality it is still so high that you won't have to worry about it if you are controlling it from a microcontroller. Operational amplifiers are not usually designed to provide high current output they are mainly voltage amplifiers although there are many power amplifier chips which are essentially powerful operational amplifiers. But having said that they may not have the current capability you are looking for. If you are looking to use a H bridge then you probably don't need an operational amplifier. You will need for MOSFETs to end channel and 2 P channel MOSFETs. You can also use for N channel ones but that will be complicating things at this stage. MOSFETs also have very high input impedance so they can easily be driven straight from a microcontroller. You will need to use on the low side (the N channel MOSFETs) logic level MOSFETs as these can be fully switched on with just 5 V as their threshold voltage will be in the region of 1 to 2 V. Each low side MOSFET can also be used it corresponding highside MOSFET although you don't get the fastest response by doing this but it's a simple circuit solution. You may need to use MOSFET driver ICs which will be able to switch the MOSFET correctly at high speed although as somebody else has said getting an actual H bridge chip may be easier and cheaper. |
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