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| Everything goes wrong in my analog circuit |
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| Eldi4:
Hello there, I've been trying to build some analog line following robot, the design was based on http://www.will-moore.com/analog-line-follower after some tweaking on the circuit i started building it, I used TL084 instead of OPA4727, and think it should do just fine, but after building the whole circuit i found problems, here is the list of the problems : 1. TL084 output only swing 0.6V~3.7V with 5V supply voltage, i know TL084 is not a rail to rail output op-amp but i really did'nt expect it to be this worse, if you have any recommendation on jellybean op-amp that is better than TL084 please tell me. 2. The differential op-amp on the sensor gain was huge (it is supposed to unity gain),it's just swinging to 0.6V or 3.7V (not in between). When i measure the resistance of the summing resistor of the sensor it say 28k (I use 100k instead of 470k), is it the problem?. After giving voltage follower on the sensor's output the differential op-amp seems to work fine, but i doubt it still :palm:. 3. The Triangle Wave generator does'nt work, it just give plain 3.7V DC, i have pretty much checked any connection of the ic but it still does'nt work, the way i check the triangle wave generator is connecting them to speaker input (as i dont have an oscilloscope), and the speaker only sounds "dug" once when i connect or disconnect the triangle wave output to speaker's input. Pin 2 and 5 voltage shows 2.5V (5V Supply), pin 1 0.6V, pin 3 2.1V, pin 6 0.6V, pin 7 3.7V I have not checked other op-amps behavior, because those three already confuses me for 4 days, and i'm sure there are other unrevealed problems too :palm: Mine version of schematic is on the attachment, |
| rstofer:
--- Quote from: Eldi4 on March 09, 2019, 08:29:43 am ---Hello there, I've been trying to build some analog line following robot, the design was based on http://www.will-moore.com/analog-line-follower after some tweaking on the circuit i started building it, I used TL084 instead of OPA4727, and think it should do just fine, but after building the whole circuit i found problems, here is the list of the problems : 1. TL084 output only swing 0.6V~3.7V with 5V supply voltage, i know TL084 is not a rail to rail output op-amp but i really did'nt expect it to be this worse, if you have any recommendation on jellybean op-amp that is better than TL084 please tell me. --- End quote --- The datasheet shows a worst case swing of +-12V when the TL084 operates on a +-15V supply. So, worst case, it can't get within 3 volts of the rails. I'm surprised it even operates on a 5V supply. See VOM on page 6 http://www.ti.com/lit/ds/symlink/tl081.pdf --- Quote ---2. The differential op-amp on the sensor gain was huge (it is supposed to unity gain),it's just swinging to 0.6V or 3.7V (not in between). When i measure the resistance of the summing resistor of the sensor it say 28k (I use 100k instead of 470k), is it the problem?. After giving voltage follower on the sensor's output the differential op-amp seems to work fine, but i doubt it still :palm:. --- End quote --- Op amp 3B has positive feedback (the feedback resistor is connected to the + input) so all it will ever do is switch between minimum and maximum output voltages. The note mentions hysteresis. Op amp 2B doesn't appear to have any series resistors between the sensors and the pins. The gain could be quite high if the sensor impedance is ow. Op amp 3A has a gain of around 100. --- Quote --- 3. The Triangle Wave generator does'nt work, it just give plain 3.7V DC, i have pretty much checked any connection of the ic but it still does'nt work, the way i check the triangle wave generator is connecting them to speaker input (as i dont have an oscilloscope), and the speaker only sounds "dug" once when i connect or disconnect the triangle wave output to speaker's input. Pin 2 and 5 voltage shows 2.5V (5V Supply), pin 1 0.6V, pin 3 2.1V, pin 6 0.6V, pin 7 3.7V --- End quote --- That triangle generator doesn't look right. First you need to generate a square wave and that takes at least one op amp, three resistors and a capacitor. Then you need to create the triangle wave and that is nothing more than an integrator, a couple of resistors and ANOTHER capacitor. http://www.ques10.com/p/22759/explain-triangular-wave-generator-using-opamp/ --- Quote --- I have not checked other op-amps behavior, because those three already confuses me for 4 days, and i'm sure there are other unrevealed problems too :palm: Mine version of schematic is on the attachment, --- End quote --- |
| CatalinaWOW:
I am not sure what you mean by "jelly bean". You probably can't find a $0.03 op amp for this task. The one specified is roughly four dollars. You can do a quick search for what is available in your area and find op-amps for under a dollar that look like they would work. One example: https://www.mouser.com/ProductDetail/Renesas-Intersil/EL5111TIWTZ-T7A?qs=sGAEpiMZZMtOXy69nW9rMwWeYYZE9XJK%2F%252BbJZK77xYE%3D I can see how the triangle generator might work. The second op-amp acts as a comparator to flip the charge on the capacitor. The use of a parallel 470k and 20k resistor to get the specified 19k resistance (see the second schematic in your link) suggests that some tuning may be required. Other things in the link article suggest that while this circuit works it requires some tuning. You can probably get the needed oscilloscope functionality out of one of the many free oscilloscope programs that use the computer sound card for input. They are crude, but will let you look at a lot more of what is happening. |
| rstofer:
--- Quote from: CatalinaWOW on March 09, 2019, 05:29:54 pm ---I can see how the triangle generator might work. The second op-amp acts as a comparator to flip the charge on the capacitor. The use of a parallel 470k and 20k resistor to get the specified 19k resistance (see the second schematic in your link) suggests that some tuning may be required. Other things in the link article suggest that while this circuit works it requires some tuning. You can probably get the needed oscilloscope functionality out of one of the many free oscilloscope programs that use the computer sound card for input. They are crude, but will let you look at a lot more of what is happening. --- End quote --- And it required tuning for the more expensive, and capable, op amps. The chances that the tuning, as shown in the original schematic, will work with the selected op amps is questionable. |
| Wimberleytech:
--- Quote from: Eldi4 on March 09, 2019, 08:29:43 am ---3. The Triangle Wave generator does'nt work, it just give plain 3.7V DC, i have pretty much checked any connection of the ic but it still does'nt work, the way i check the triangle wave generator is connecting them to speaker input (as i dont have an oscilloscope), and the speaker only sounds "dug" once when i connect or disconnect the triangle wave output to speaker's input. Pin 2 and 5 voltage shows 2.5V (5V Supply), pin 1 0.6V, pin 3 2.1V, pin 6 0.6V, pin 7 3.7V --- End quote --- The triangle wave generator will work with ideal components with the values given. However, not with the opamp you have chosen. Change R2 to 10K and see what happens. Here is the circuit drawn a different way...I prefer the signal flow...integrator to a comparator then fed back. Just my preference. |
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