| Electronics > Beginners |
| Portable Low Frequency square wave generator circuit - Solved - page 3 |
| (1/16) > >> |
| Laszlo:
Hi, I am a locomotive test engineer and I could use a portable square wave generator which could output a 12Vp-p square wave from 1 to 1000Hz, with an input impedance of 50ohms and of course 50% duty cycle. Reason being, with that signal some trainborne equipment, can be tricked to believe that the loco is running (speedo, WSP etc..) So I tried relentlessly with my zero electronics knowledge to build up a circuit using a 555 timer ic with very little success. - I could only produce signals with positive peaks, and couldn't get the ac coupling to work, also the best I could achieve is 53% duty cycle. (https://mintelectronics.wordpress.com/2012/06/17/squarewave-generator-using-555/) - Using this circuit. Tried an LM741 op-amp, but hey, I couldn't even figure it out how to power it up with the dual PSU. So I gave up and bought this DIY sig gen kit from aliexpress, which works like a charm, but it has an input impedance of a whopping 800 ohms plus. Also, I doubt that it would be beefy enough to provide enough current for my line of work. My question is whether anyone on this forum knows about a working circuit which I could utilize to build my little project. All answers are much appreciated. Laszlo |
| nsrmagazin:
What is the tolerance on the frequency, duty cycle, voltage and current? See the circuit for "50% Duty Cycle Astable Oscillator" or "Improved 555 Oscillator Duty Cycle". https://www.electronics-tutorials.ws/waveforms/555_oscillator.html With opamps its the easiest. https://www.electronics-tutorials.ws/opamp/op-amp-multivibrator.html Can not be done with a single timer555 IC. The timer has a maximum output of "15VDC"(real "12VDC"). Is using a microcontroller an option? It will be easier to switch a transistor or should I say 2 complementary transistors. Last option is a H bridge(most commonly used, hardest and best). This thread summarizes the opamp option: https://www.edaboard.com/showthread.php?292062-Dual-polarity-square-wave-generator |
| beanflying:
Few questions. Does it need to be portable or do you have a voltage source available, if you have a source what is it? I am getting the idea you are looking for +-6V or 12p-p because you use the term ac coupling? Or do you mean you want a 0-12V pulse? Not a big deal either way but it does matter. To keep it simple and the explanation too (until you give a few more details) an arduino micro with a display of some sort (if needed) driving an output Transistor or FET would give you maximum variation and simple electronics. Now we need to know your power supply options and the output you need :) The dead simple version with no bells and whistles (bad train pun :palm: ) is a multivibrator such as in this link https://www.electronics-tutorials.ws/waveforms/astable.html Or re look at the 555 option depending on those couple of questions. |
| spec:
--- Quote from: Laszlo on January 26, 2019, 08:22:34 pm ---Hi, I am a locomotive test engineer and I could use a portable square wave generator which could output a 12Vp-p square wave from 1 to 1000Hz, with an input [output] impedance of 50ohms and of course 50% duty cycle. Reason being, with that signal some trainborne equipment, can be tricked to believe that the loco is running (speedo, WSP etc..) So I tried relentlessly with my zero electronics knowledge to build up a circuit using a 555 timer ic with very little success. - I could only produce signals with positive peaks, and couldn't get the ac coupling to work, also the best I could achieve is 53% duty cycle. (https://mintelectronics.wordpress.com/2012/06/17/squarewave-generator-using-555/) - Using this circuit. Tried an LM741 op-amp, but hey, I couldn't even figure it out how to power it up with the dual PSU. So I gave up and bought this DIY sig gen kit from aliexpress, which works like a charm, but it has an input [output] impedance of a whopping 800 ohms plus. Also, I doubt that it would be beefy enough to provide enough current for my line of work. --- End quote --- Hi Laszlo, (I have taken the liberty of altering your original post(OP) above, about inputs and outputs, to express what I think you intended.) You could use a 555 or possibly the Aliexpress signal generator to do your job, but it sounds like you would need to add an output driver circuit, which is quite straight forward. But as has been stated, we need to know what power source you are using, battery or mains, I would guess battery in view of the application. Also, we need to know the positive excursion and negative excursion of the output waveform required from the signal generator. I take it, from what you say, that the input impedance of the units under test (UUT) is 50 Ohms. --- Quote from: Laszlo on January 26, 2019, 08:22:34 pm ---My question is whether anyone on this forum knows about a working circuit which I could utilize to build my little project. --- End quote --- Yes: once we know your requirements, we will be in a position to post a complete circuit that will do your job nicely. :) |
| Zero999:
--- Quote from: Laszlo on January 26, 2019, 08:22:34 pm ---Hi, I am a locomotive test engineer and I could use a portable square wave generator which could output a 12Vp-p square wave from 1 to 1000Hz, with an input impedance of 50ohms and of course 50% duty cycle. Reason being, with that signal some trainborne equipment, can be tricked to believe that the loco is running (speedo, WSP etc..) So I tried relentlessly with my zero electronics knowledge to build up a circuit using a 555 timer ic with very little success. - I could only produce signals with positive peaks, and couldn't get the ac coupling to work, also the best I could achieve is 53% duty cycle. (https://mintelectronics.wordpress.com/2012/06/17/squarewave-generator-using-555/) - Using this circuit. Tried an LM741 op-amp, but hey, I couldn't even figure it out how to power it up with the dual PSU. So I gave up and bought this DIY sig gen kit from aliexpress, which works like a charm, but it has an input impedance of a whopping 800 ohms plus. Also, I doubt that it would be beefy enough to provide enough current for my line of work. My question is whether anyone on this forum knows about a working circuit which I could utilize to build my little project. All answers are much appreciated. Laszlo --- End quote --- I think you've got your impedances mixed up. Don't you mean you need an output impedance of 50Ω? You need some sort of buffer to get the impedance down to the desired level. The TC4420 will do. It has a much lower output impedance than 50R so will need a series resistor on the output. https://ww1.microchip.com/downloads/en/DeviceDoc/21419D.pdf Add the MOSFET driver IC to your existing signal generator or build your own using a microcontroller or Schmitt trigger. Another possibility is to build a higher frequency astable and add a frequency divider to get exactly 50% duty cycle. |
| Navigation |
| Message Index |
| Next page |