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Circuit idea/op-amp investing voltage-to-current converterlite adx forex tsd
V to I converter op-amp - Voltage to current converter( With floating load and with grounded load)CRYPTO COMMODITIES
We prefer the last one. Do not consider the ohmic non linear effects. Basic non-electrical idea: Removing a disturbance by an "antidisturbance"[ edit edit source ] Let see the polarity of disturbance in "passive" picture. As we know the output of an op-amp is a voltage source ,but it's input a current source. Voltage source has small infinite resistance, ideally zero, but in reality fractions of ohms, even ohms. The Norton replacement of current source with voltage source series with a high resistance equal with in-between armature resistance make the op-amp feasible.
The device remains on until the sensitive in quadrant IV. Some triacs There are a couple of scenarios in main current falls below the holding cannot be triggered in quadrant IV. The first is simply by applying in Fig. The second scenario occurs when the with a relatively small voltage applied trigger option against sensitivity to triac tries to turn off with an inductive to its main terminals.
The resulting voltage spike from terminal voltage. The circuit in Fig. The gate current must also In addition to the snubber, which will because the current through the device be applied for sufficient time to protect the triac from fast transients at will drop below the holding current turn on the triac. This turn on time voltages below its maximum voltage, as the AC voltage drops towards 0V.
This can a triac has to be triggered during every microseconds. The specified time will be achieved by a metal-oxide varistor half cycle of the AC waveform. This assume a large voltage across the triac, MOV. These exhibit a very high happens automatically in the circuit but if the trigger pulse is applied early resistance up to their varistor voltage, in Fig. This is the photosensitive diac device will for longer to ensure that the triac is somewhat similar to a diode switch- trigger directly from the AC supply in on, but occurs for voltages of either every cycle.
Loss of fourth-quadrant cycle at which the device is triggered triggering in these devices is not a this is known as phase control. The MT1 MT1 major problem because most triac later the power is switched on the less circuits do not use triggering in the power is delivered to the load.
MT2 MT2 fourth quadrant anyway. This simply means by gate currents of either polarity leads Fig. Creepage Fig. Triac circuit with snubber Rs and Cs to prevent false triggering and MOV for is the shortage path between two overvoltage protection conductive parts measured along the surface of the circuit board. Creepage switch the triac at any point in the will provide some guidance. The circuit is important because it is easy for the AC cycle. It distinguishes We have looked at a few examples of opto-isolated circuit by cutting a slot in these components from opto-isolators opto-isolated triac power switches; the PCB underneath the opto-isolator with built-in zero-crossing detection.
This Other manufactures use different terms of power switching than just including significantly increases the creepage — for example, Vishay simply use the an opto-isolator in the schematic. For but not the clearance. Random phase, or non-zero crossing opto-isolators are required Fig.
Note that although the photo-sensitive device symbol looks like a triac it is not intended for direct switching of a load. This and similar devices are intended for triggering of power triacs. Use of zero-crossing detection means that the load is switch as the AC supply goes through zero volts. This reduces surge currents to the load and decreases the electromagnetic interference EMI caused by the load switching. As would also be the case for the circuits in Fig.
The required forward current can be found by consulting the datasheet — it will be different for different devices, but typically in the order of milliamps. Typical snubber values are also shown, although the snubber may not be needed in all situations and for others different values will be required; again the datasheet 56 Everyday Practical Electronics, January Circuit Surgery JAN Problem sourcing software?
Generaic l tr o n s Elec t cha I Can help! Visit our component packed website for a vast range of parts - old and new, many unavailable elsewhere! This is actu- all the time — but sometimes it comes in handy. Your main appli- affecting the accuracy of our results. Our template code already enables them in the main function. Going back to our equation for total conversion time, this gives us a time of: Interrupts Handling the interrupt is more complicated, as we need to 2. Fortunately, That equates to a sampling frequency of 98kHz.
This is a the basics of this have already been provided in the tem- maximum theoretical limit and our real sample rate will plate code, in the file interrupts. We have to integrate be limited by our choice of processor oscillator frequency our ADC handler into this function however, as it cur- and how fast we can process the data in our main applica- rently handles just the timer interrupt.
At the moment, the tion — much slower if we are running a Fourier transform code looks like: algorithm, for example. The template code has been updated void interrupt InterruptHandler void and an interrupt version of the potenti- ometer code added. Our example circuit from last PIR1bits. We need to improve this now to test for any number of What can we do with the ADC peripheral, besides read- interrupt sources, starting with our ADC interrupt. The sim- ing a potentiometer?
A really great use is to measure the in- plest way is with an if statement: ternal reference voltage source of the processor so you can determine the supply voltage perfect for battery-powered void interrupt InterruptHandler void applications. The board, shown in Fig. With the backing of people through dled by adding further else if statements.
By the time you read this the boards should This code is in the adc. The processor, however, notices that an interrupt flag is still active and will immedi- ately re-invoke the main interrupt routine. First, the value of TACQT needs to be calculated, and this will be depend on the output impedance of your input sig- nal source and the supply voltage and temperature of the Fig.
There is an equation for this on page of the data- sheet. Hibbett, and from his blog at mjhdesigns. More recently, digital displays as opposed to the older kind. If you are purchasing a have taken center stage. In this context, we can consider the processed.
A simple glance at tive than a 1mA meter, for example. Driving your meter Apart from anything else, I like using analogue me- In the fullness of time, we will want to display data on ters for my hobby projects because they offer a certain our meter s.
This data may be generated algorithmi- sense of style. And as I mentioned in a previous col- cally by software, or it may reflect the state of a sen- umn, one of my current projects is to create a Vetinari sor. But before we reach that point, we need to ensure Clock using a large meter to represent the hours from that we can control our meter. Consider the circuit 1 to 12; two medium-sized meters to display the min- and associated Arduino code shown below.
When you rotate discussions we will assume means using an Arduino the pot from one extreme to the other, the value should Uno with a 5V power supply. If you agree with me, but your setup is working the opposite way, simply swap the 5V and GND con- nections to the pot and all will be well. Resistance is futile! This meter will have an internal re- sistance we might call Rcoil. Note that a new meter determine this nugget on knowledge. Turn that you can burn out the coil using a multimeter to try the potentiometer anticlockwise to its zero value and to measure the resistance.
We know our actual Rtotal val- this assumption. If our total resistance reaches its FSD. The next value down in sume that this value is Upload this new program into the Arduino. Now, ro- tating the potentiometer fully clockwise will cause the meter to just achieve its FSD. Until next time, have a good one! Introduction subjects that will interest everyone involved in electronics, from The Teach-In 4 CD-ROM covers three of the most important This Teach-In series of articles was originally published hobbyists and students to professionals.
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Unlike traditional CAD programs that make use of components with lifelike images rather than abstract abstract symbols and notations, Fritzing uses whenever symbols. Links to tutorials, videos and user forums are possible lifelike images. That can be Open source for hobbyists gained through experimentation, chatting to people on The release of the program as open source is significant, the friendly web forums or by watching the wide range it means you have free access to the source code, and can of video tutorials covering the use of the tool itself and make changes if you wish.
While this is not a practical electronics in general. Components, wires, modules and changes. Development is driven by the desire to improve breadboard images look like the real things, and creating a Everyday 65 Everyday Practical Practical Electronics, Electronics, JanuaryAugust 65 Fritzing article. The Fritzing application start-up screen Fig. One of the many sample projects circuit by dragging these items around the screen is about as lifelike as it is going to get in a virtual design environ- ment.
You really feel like you are making something with physical components, and it helps you identify with what you are creating. Traditional CAD programs display the circuit in a more abstract manner, making the schematic entry more efficient but far less fun. Documenting your projects Fritzing is a great tool for documenting your one-off pro- jects. By using real-life representations of components you are not forced to learn and remember abstract sym- bols.
Once created, the pictures of the designs are even beautified! The design can then be exported as an image, which you would be proud to share by email or on a web blog. Take the image of one of my most recent projects, in Fig. This consists of three components — a microcon- troller board, an LCD display and a variable resistor.
No Fig. Now have a look at a design of similar After you have documented your design as a schematic of complexity expressed within Fritzing, in Fig. There in if necessary. The components are stored within the are no options to automatically place the components, but program in a scalable vector graphic format. The normal schematic for trial and error, either through experimenting or by studying this design is available if required, as in Fig. What you do get, however, is verification that your components are correctly joined together.
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Now you can fix this with our Audio Delay. Reflow Kit V3 T: E: sales jpgelectronics. Distributed by Seymour, 86 Newman St. Email: subs epemag. All other trademarks mentioned herein are the property of their respective companies. All rights reserved. There is a problem with the rectifier turning on slowly, because Vout has to move all the way from the top rail down to the bias voltage, and the op amp has a slew-rate limitation. This phenomenon can be seen more clearly at a higher frequency:.
The turn-on delay does not vary much with the input resistance, unlike the turn-off overshoot. I believe that the overshoot as the rectifier turns off is due to capacitance, as adding a small feedback capacitor in parallel with the diode increases the overshoot substantially:. The turn-on delay is masked somewhat by the high-frequency feedback. Note: the S has the best high-frequency response if you consider 15kHZ high frequency of any of the transistors I looked, probably because it has the lowest capacitance.
I should be able to get better range by using a fast-response Schottky diode instead of diode-connected transistor. Yesterday, I spent the day testing different transistors in the log amplifier , to see whether it made much difference which transistor I used. Here is the test circuit I made essentially the same as for the tests in Logarithmic amplifier again :. The op amp at the top is a unity-gain buffer to provide a steady Vbias source that capable of providing some current unlike the TLILP voltage reference shown here as an adjustable Zener diode.
The nominal 2. The unity-gain buffer on the left is to make the load on the RC circuit as high impedance as possible, so as not to disrupt the RC charging or discharging. The parallel resistance of the capacitor makes the destination voltage of the RC circuit slightly lower than V bias , which means that we will not get all the way to V bias when testing PNP transistors, but will overshoot slightly when testing NPN transistors.
I made some measurements with V out but most with the 3V out signal. The scaling factor was 3. The middle op amp is the log amplifier itself, which relies on the exponential relationship of the emitter current to the voltage across the base-emitter junction. More precisely, we can use the Ebers-Moll model of a bipolar transistor to get.
The collector is held at Vbias by the feedback loop of the op amp, so V BC is zero, simplifying the equation to. I might also run into effects not included in the Ebers-Moll model, especially at very large or very small collector currents. Adjusting R 2 to change the current can move the output offset around.
If I make R 2 large and the current small, then V BE will be small, and the approximation will be poor. If I make R 2 small, the current may exceed what the transistor is designed for and there may be saturation effects. The exponential decay of the capacitor to about V bias allows us to extend the range of the fit well past the resolution of the ADC to measure V in or V bias. Combining the formulas for the log amplifier and the RC discharge gives us the general formula. Fitting the constants for this turns out to be difficult, because v 3 is close to zero.
If it were exactly zero, the formula would be , and we could make arbitrary tradeoffs between v 2 and RC. We can get a nice plot of V out vs. The upward tail shows where the collector-base junction begins to be forward biased, and the current is no longer controlled by the base-emitter voltage. Note that this curve shows that the problems we had with direct measurement of RC discharge curves in the physics lab was due to limitations of the Arduino ADC, not to the underlying RC circuit.
The tails of the discharge continue to follow the exponential well beyond the resolution of the bit ADC in the Arduino. Of course, I picked out the S plot to show, because it was the nicest one. Some of the others were weird. I have no idea what causes this flat spot. The larger resistor gives a somewhat softer turn on for the transistor if we go past Vbias. I got better dynamic ranges for the NPN transistors than for the PNP transistors, but this may have been due to artifacts of the test setup.
In any case, it looks like 60—70dB ranges are fairly easily achieved. So the better dynamic range of the NPN was just an artifact of my test setup, as I thought. If one were to try to make a measuring instrument with a log amplifier, there would have to be some temperature compensation as the log-amplifier offset and scaling are both temperature sensitive.
Having a temperature-independent voltage source for calibration would be a good idea. Yesterday, in Logarithmic amplifier , I ended with the following plot:. I was bothered by the broad cloud of points, and wanted to come up with a better test circuit—one that would give me more confidence in the parameters.
It was also quite difficult to get close to Vbias—the closest this could measure was one least-significant-bit of the DAC away about 5mV. A factor of from the largest to the smallest signal is 54dB, but only about the upper 40dB of that was good enough data for fitting and very little time was spent at near the Vbias value.
I decided to use a very simple slow-changing signal: a capacitor charging toward Vbias through a large resistor. Output voltage from log amplifier with 3x gain in second stage as capacitor charges. What are the weird glitches? The capacitor charging should be a smooth curve exponential decay to Vbias, so the log amplifier output should be a straight line with time. There were two obvious problems with this first data—the output was not a straight line and there were weird glitches about every 15—20 seconds.
The non-straight curve comes from the capacitor not charging to Vbias. Even when the capacitor was given lots of time to charge, it remained stubbornly below the desired voltage. In think that the problem is leakage current: resistance in parallel with the capacitor. I can well believe that I have sneak paths with that sort of resistance on the breadboard as well as in the capacitor. The glitches had a different explanation: they were not glitches in the log amplifier circuit, but in the 5V power supply being used as a reference for the ADC on the Arduino board—I had forgotten how bad the USB power is coming out of my laptop, though I had certainly observed the 5V supply dropping for a second about every 20 seconds on previous projects.
The drop in the reference for the ADC results in a bogus increase in the measured voltages. Again the blue fit uses the measured Vin and Vbias voltages, while the green curve tries to fit an RC decay model. Note the digitization noise on the measured inputs towards the end of the charging time. To solve the problem of the leakage currents, I tried going to a larger capacitor and smaller resistor to get a similar RC time constant. At that point I had not found and read the Cornell Dublier application note, though I suspected that the parallel resistance might scale inversely with the capacitor size, in which case I would be facing the same problem no matter how I chose the R-vs-C tradeoff.
Only reducing the RC time constant would work for getting me closer to Vbias. The green fit using an RC charge model does not seem quite as good a fit. The calibration of 9. I then tried a smaller RC time constant hoping that the larger current with the same capacitor would result in getting closer to Vbias, and so testing a larger dynamic range on the log amplifier. I found it difficult to fit parameters for modeling the RC charge the green fit.
The blue curve fits better up to about 65 seconds, then has quantization problems. Using that estimate of 9. Note: the parallel resistance of the capacitors would not explain the not-quite-exponential behavior we saw in the RC time constant lab , since those measurements were discharging the capacitor to zero. A parallel resistance would just change the time constant, not the final voltage. I was using the Duemilanove board for the log-amplifier tests.
I retried with the Uno board, to see if differences in the ADC linearity make a difference in the fit:. The missing parts of the blue curve are where the Uno board read the input as having passed Vbias. The mV range over seconds corresponds to about 69dB, assuming that the 9. Anyone have any ideas? Incidentally, my son has decided not to include a microphone in his project. The silicon MEMS mic was small enough, but the op amp chip for the analog processing was too big for the small board area he had left in his layout, and he decided that the loudness detector was not valuable enough for the board area and parts cost.
I believe that his available board area shrunk a little today, because he discovered that the keep-away check had not been turned on in the Eagle design-rule checker. Turning it on indicated that he had packed the capacitors too close in places, and he had to spread them out. My son wanted to design a circuit to convert microphone inputs to loudness measurements usable by an Arduino or other ATMega processor.
We discussed the idea together, coming up with a few different ideas. The simplest approach would be to amplify the microphone then do everything digitally on the Arduino. There are several features of this approach:. Although the mostly digital solution has not been completely ruled out, he wanted to know what was possible with analog circuits. We looked at two main choices:. Block diagram of the loudness circuit.
We then spent some time reading on the web how to make good rectifier circuits and logarithmic amplifiers. My son wanted to know what the output range of the log amplifier would be and whether he would need another stage of amplification after the log amplifier. Unfortunately, the theory of the log amplifier uses the Shockley ideal diode equation , which needs the saturation current of the pn junction—not something that is reported for transistors.
Today I decided to build a log amplifier and see if I could measure the output. I also wanted to figure out what sort of dynamic range he could get from a log amp. Here is the circuit I ended up with, after some tweaking of parameters:. The top circuit is just a bias voltage generator to create a reference voltage from a single supply. He might want to use a 1. The bottom circuit is the log amplifier itself.
I chose a PNP transistor so that Vout would be more positive as the input current got further from Vbias. I have 6 different PNP transistors from the Iteadstudio assortment of 11 different transistors , and I chose the A rather arbitrarily, because it had the lowest current gain. I should probably try each of the other PNP transistors in this circuit, to see how sensitive the circuit is to the transistor characteristics. I suspect it is very sensitive to them.
The circuit only works if the collector-base junction is reverse-biased the usual case for bipolar transistors , so that the collector current is determined by the base current. The emitter-base junction may be either forward or reverse biased. Note that if Vin is larger than Vbias, the collector-base junction becomes forward-biased, the negative input of the op amp is slightly above Vbias, and the op amp output hits the bottom rail.
As long as Vin stays below Vbias, the current through R2 should be , and the output voltage should be for some constants A and B that depend on the transistor. Note that changing R2 just changes the offset of the output, not the scaling, so the range of the output is not adjustable without a subsequent amplifier. The pF capacitor across the transistor was not part of the designs I saw on the web, but I needed to add it to suppress high-frequency around 3MHz oscillations that occurred.
The oscillations were strongest when the current through R2 was large, and the log output high. I first tried adding a base-emitter capacitor, which eliminated the oscillations, but I still has some lower-frequency oscillations when the transistor was shutting off very low currents. Moving the capacitor to be across the whole transistor as shown in the schematic cleaned up both problems.
I put ramp and sine wave inputs into the log amplifier. The waveforms were generated with the Bitscope function generator, which does not allow setting the offset very precisely—there is only an 8-bit DAC generating the waveform. Here is a sample waveform:.
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