Scullcom Hobby Electronics #42 - Design & Build a Pulse Generator Part 1

[@blink-klippie]

A very comprehensive and useful project. It's nice to see a project from start to finish and then find everything you need to be able to duplicate it at home. Very well done and thank you. Kind regards Paul.

[@scullcomhobbyelectronics1702]

Thanks Paul.

[@calabrese1531]

Great video as usual, very interesting analysis of the LTC6992 IC. I can't wait to see the finished project and the capabilities of this generator which, no doubt about it, are many. With the hope of finding more about the LTC6992 IC , I clicked on the links you provided and found out that the homepage of your website is not about electronics but Comics and Artworks done by you. I didn't know you were such a good artist. To all the people that may read this long comment, I highly recommend the reading of the World of Genesis.

[@scullcomhobbyelectronics1702]

Thanks for your comments. My scullcom.com website is where I host some on my son's artwork and comics he writes. I use scullcom.com to also hold download links for my projects. You will find my electronics website at www.scullcom.uk this is where I post details on my electronics projects.

[@dpavlin]

Thank you very much for your step by step description of project, and I must say that most useful part (for me) is problems which you find and solve during construction.

[@scullcomhobbyelectronics1702]

Thanks for your comment.

[@cncdavenz]

Another very good project. Thanks for your dedication to the hobby. Cheers Dave

[@scullcomhobbyelectronics1702]

Thanks. By the way the name is Louis. You may have got the name Dave from my scullcom.com website where I have posted some of my youngest son David's artwork and comics. He is the artist in the family :)

[@priestblood]

Fantastic project,what a great video,I wish everyone would explain and build like this ,Top job.Thanks for sharing & as always stay healthy

[@supyrow]

the LTC6992 is a awesome part! very versatile! Thanks for the ideas! 73!

[@scullcomhobbyelectronics1702]

Thanks. I try to introduce different IC options in my projects and do things a different way so we can learn about what is available that could also be used in other projects.

[@kose2ik]

Why do not you use good PCB design? 25:29 9V & 5v thicker rails (but especially GND. They will also be part of the heatsink 5v regulator). But I'm very grateful to you and I thank you that you have done a lot of teaching and instructional tutorial videos on KZbin!

[@kose2ik]

i think thin rails is termo (-stress) sensitive. ( I think this modification is better goo.gl/photos/z8aKM9MgsFW7RYhb6 and output wires and pads is thicker/bigger )

[@sean999ification]

I love your videos.

[@scullcomhobbyelectronics1702]

Thank you.

[@DavidLeeMenefee]

I second that. I wish there were more videos on the NET like these. Thumbs UP....EW

[@isidoromaich7226]

This is really great! Thank you! just a beautiful instrument to use and play, buying the parts to start to build asap

[@scullcomhobbyelectronics1702]

Thanks.

[@javierpallalorden]

Thanks! Do you know if we could use a digital potentiometer (with Arduino-SPI) like the MCP41100 for trimming the frequency? That way we could set all with a rotary encoder.

[@scullcomhobbyelectronics1702]

I have been looking at other ways of setting the frequency and one is to test a digital potentiometer IC so I will be testing this as an option. I am also looking at other possibilities since I have found that at higher frequencies just using a standard pot can cause jitter.

[@FlyingShotsman]

Nice project -- you very neatly integrated several ICs to achieve what you wanted. / I may have misunderstood your description, but I think you said the "polarity" switch altered the output from positive to negative (presumably with respect to ground). Instead, it appears to simply invert the duty cycle. / I don't know how you'd achieve it with any accuracy using an Arduino Nano, but a readout of output frequency would be nice.

[@scullcomhobbyelectronics1702]

Thanks for your comments. As far as I can see it does invert the output polarity as the position of the duty cycle control signal remains unchanged. I supposed it all depend How you look at it. I have thought about adding a frequency reading, that was the reason I chose a larger LCD display module for this project.

[@FlyingShotsman]

Hmm... If the polarity were changing, I would expect the scope trace to go negative -- that is, for the square wave to drop below the zero volts graticule -- but it doesn't (except for a little ringing on the falling edge). If you set the duty cycle at, say, 70%, then in one switch position the square wave is high 70% of the time and in the other switch position it's low 70% of the time. So, the duty cycle percentage is being inverted, not the output polarity. Anyway, cool project; I'm looking forward to part two.

[@RobB_VK6ES]

While I do not know your future intentions for this device it seems to me using the 12bit DAC to control a 4bit divider input is rather a waste. Why not use 4 digital outputs from the arduino summed via resistors feeding a voltage divider to set the division ratio voltage? Also if you used 2 of the 12 bit DACs to replace the freq and duty pots you could make this thing programmable via a serial link for automated sweeps and duty control and use a rotary encoder for front panel control. I really like the way you present these projects with the full circuit explanation and highlighting some inovative special function ICs

[@javierpallalorden]

Using an MCP4725 as an I2C module will cost €1,30 on ebay. I would like to see a rotary encoder like a menu selection for the frequency and divider network, that way we could loose the switch etc.

[@scullcomhobbyelectronics1702]

Thanks for your comments. The reason I used the 12 bit DAC (MCP4725) was because it was low cost and also I wanted to leave as many of the Arduino Nano data pins free for future upgrades and options. Also the MCP4725 has some internal EEPROM memory which we could use later. Part 1 of this project was really to introduce the LTC6992 and see how we could use it. I am looking at other ways of controlling this IC make it more programmable as you suggested.

[@HennerZeller]

If we have 3 bits controlling the programmable divider, shouldn't we only have a range of 0..7 ? (the upper bit, after all, is used for the polarity).

[@scullcomhobbyelectronics1702]

Yes we only have ranges from 0 to 7 (8 frequency ranges). However, if you look at the DIVCODE programming table I show in the video you will see the DIVCODE positions from 8 to 15 require higher control voltages (see last column) for the same frequency ranges when the output polarity is changed. Therefore we are using the first 3 bits of the binary code which gives us 000 to 111 (0 to 15 positions). The 4th bit is only used for the polarity switching circuit in the IC. If you have a look at page 15 of the datasheet you will see what I am trying to explain.

[@MrHD71]

can you make a precision power supply with constant current and constant voltage

[@scullcomhobbyelectronics1702]

This could be an idea for a future project.

[@integral32gb]

I too would very much like to see this project

[@nkp5845]

I would also like to see such project. Something with very low noise suitable for both analog and digital circutis

[@jaywalt1311]

Is there a way to have the display show the current frequency?

[@scullcomhobbyelectronics1702]

This is something I already had in mind as a future upgrade to this basic project. Hence the reason I choose to use a larger LCD display so we have space to add things like a frequency reading.

[@oscarilmio7148]

Hello there. Is this project "adbandoned"?

[@bluedeath996]

I can't seem to find part 2. if you could direct me to it I would be grateful.

[@blink-klippie]

Hello, Would it be possible to drive an IRL540N mosfet with this pulse generator? What is the voltage output? Kind regards Paul.

[@scullcomhobbyelectronics1702]

As far as I can tell the IRL540N should work fine. Need to work in the DC safe operating area. I will further discuss other Mosfet options in Part 2 of this project.

[@blink-klippie]

+Scullcom Hobby Electronics Dear Sir, Thank you for the reply. Very much looking forward to part2. I had a little look at some mosfet driver chips but there are so many to choose from. I am trying to put together a pulsed power supply that can deliver up to 100VDC at 5A max , the pulse driver would be great if it could deliver 10khz to 200khz. The power supply will be used for a small wire edm machine .I guess the mosfet choice is very important for this requirement. I think your pulse generator could be perfect for my project. All the best and kind regards Paul

[@evghenim1955]

Why using 12 bit DAC while ADC inside the chip is only 4 bit?

[@scullcomhobbyelectronics1702]

The 12 bit DAC I used is low cost and also has some internal EEPROM memory we could use later in any upgrade. Also this DAC is simply controlled on the I2C bus and I wanted to introduce that on this project. Of course there are other ways of supplying this control voltage to the LTC6992 but I chose the MCP4725 for this project as it met my needs.

[@chbonnici]

How can you drive a fet with this pulse generator with an inductive load on the drain say a transformer

[@AlejandroStars]

Thank you for your excellent video, it is an interesting project, very didactic.I wonder what type of applications could have this pulse generator?

[@scullcomhobbyelectronics1702]

Thanks. You can use a pulse generator for a number of tasks. I use them when designing and developing logic circuits and testing. Also you can use one together with an oscilloscope to measure the length of a piece of coax transmission line as well as estimate its impedance. You can determine the location of a break in coax cables making it easy to locate where the break is.

[@Ziplock9000]

I notice you're getting a lot of overshoot and undershoot. Did you fix this and how?

[@scullcomhobbyelectronics1702]

Hi John, This project is not finished yet as I was distracted with some other projects. I plan to get back to this later and provide a part 2 with updates. Regards, Louis

[@zx8401ztv]

Thats a clever design, im not into using micro controllers so the option to feed the ltc6992 with switched resistors would appeal to me :-), The ltc6992 looks lika a very simple chip to use :-D.

[@scullcomhobbyelectronics1702]

Thanks. I was playing around with this IC and thought it would be a good idea for a project. The only thing I am finding the that using a variable resistor on pin 3 to control the frequency causes some instability or jitter at the higher frequencies. This is due to the longer connecting wire from the pot to the IC pin which introduces some capacitive effect. I am looking at some alternative ways to replace the variable pot, may be a digital potentiometer IC placed close to the LTC6992 on the PCB and then controlled by the Arduino Nano.

[@zx8401ztv]

What about a short length of Rg58 coaxial cable, a short length should have very little capacitance, have you tryed that? :-)

[@scullcomhobbyelectronics1702]

I could give it a try. But I would imagine even the small capacitance effects of about 20pF would still cause problems for the LTC6992. The IC would normally have a fixed resistor positioned as close as possible to pin 3. I will have a look at a few options and see what is possible.

[@dani777dani]

part2?

[@scullcomhobbyelectronics1702]

Hi, I got distracted with some other projects. I intend to come back to this project later.

[@mevlutcagdas8810]

grand master 12v mppt battery charger pls

[@chbonnici]

practical circuit I mean