4 ms·

It's not really a function generator without DC offset and proper amplitude control. I don't want to be overly negative, it's a cool project. I think there's de

It's not really a function generator without DC offset and proper amplitude control. I don't want to be overly negative, it's a cool project. I think there's definitely something to be said about having polished interface to a low end function generator. However, there needs to be more information on specification such as ENOB, sample rate, max Vpp, max offset and bandwidth.

polishdude20 6y ago
Wouldn't that be pretty easy to do as well? The most crude way to have a DC offset is to just pipe the output through a voltage divider with a potentiometer no? As for amplitude control, an op amp can be used again with a potentiometer to control the resistors needed for a specific gain right?
- jmwilson 6y ago
  Sure, the voltage divider works ... if the load impedance is high. Not a good idea for a 50 Ω load. Op amp needs a dual-rail power supply, so it needs some auxiliary power, then power electronics to get both rails. Stuff starts to get complicated, and now that $1500 Keysight box starts to looks worth its price...
  - glitchc 6y ago
    This. A function generator is not a trivial piece of digital electronics. It's a complex, highly analog beast, where the digital component of the circuit is actually rather small. Nowadays a dedicated IC (such as the XR2206) is the starting point for a home-made FG. Here's one kit: http://electronics-diy.com/electronic_schematic.php?id=128 http://electronics-diy.com/electronic_schematic.php?id=128
    - cushychicken 6y ago
      I'd even argue that the XR2206 is pretty obsolete when it comes to function generation methodologies. For one thing, it's very limited in frequency - 1MHz max, and dependent on analog components to generate it. For another thing, it's really limited in waveform types. Practically, you can only generate sine, triangle, and square waves. Modulation is possible, but requires extra hardware to pull off. The advantage I see of the DDS is that, once the signal generation portion of the product is software based, you can push upgrades to functionality via software updates. Not something any XR2206 can do!
- aDfbrtVt 6y ago
  In theory yes. The issue is the different load conditions will mess with the voltage divider bias. Check out page 272 and onward of the HP33120A manual https://coupp-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=206&filename=hp_33120a.pdf&version=1 https://coupp-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=206&...
  - jacquesm 6y ago
    Why compare a commercially available top of the line function generator with a hobby project? At this level you can add a couple of simple components and get 95% of the functionality and accuracy of the commercial one for a couple of bucks. Go higher than that and you might as well shell out the money for an army surplus one, but that does not get you what he wanted: an opportunity to tinker and learn.
    - cushychicken 6y ago
      Why compare a commercially available top of the line function generator with a hobby project? Because as soon as you do, you start to realize that you can get quite a ways with commodity hardware. Hence, why I started this project. The research I've done on the frontend of this on what's available in the market suggests to me that there's a niche for something that's a little cheaper, and a little easier to use. I also have a hunch that portability is a nice feature for most folks as well. (Hi Jacques!)
      - jacquesm 6y ago
        There is a whole branch of Chinese manufactured pc peripherals aimed squarely at this space, digital scopes, spectrum analyzers and so on, don't they make a function generator?
        cushychicken 6y ago
        They do, but the usability leaves something to be desired.
      - 6y ago
cushychicken 6y ago
Hi! Author here. You are absolutely right, and I called out a lot of those limitations in my original design doc. http://cushychicken.github.io/bfunc-design-doc/ http://cushychicken.github.io/bfunc-design-doc/ I'm just starting to get to work on the second version of this board, and I'm planning on addressing all of these in that design.

polishdude20 6y ago

Wouldn't that be pretty easy to do as well? The most crude way to have a DC offset is to just pipe the output through a voltage divider with a potentiometer no? As for amplitude control, an op amp can be used again with a potentiometer to control the resistors needed for a specific gain right?

jmwilson 6y ago
Sure, the voltage divider works ... if the load impedance is high. Not a good idea for a 50 Ω load. Op amp needs a dual-rail power supply, so it needs some auxiliary power, then power electronics to get both rails. Stuff starts to get complicated, and now that $1500 Keysight box starts to looks worth its price...
- glitchc 6y ago
  This. A function generator is not a trivial piece of digital electronics. It's a complex, highly analog beast, where the digital component of the circuit is actually rather small. Nowadays a dedicated IC (such as the XR2206) is the starting point for a home-made FG. Here's one kit: http://electronics-diy.com/electronic_schematic.php?id=128 http://electronics-diy.com/electronic_schematic.php?id=128
  - cushychicken 6y ago
    I'd even argue that the XR2206 is pretty obsolete when it comes to function generation methodologies. For one thing, it's very limited in frequency - 1MHz max, and dependent on analog components to generate it. For another thing, it's really limited in waveform types. Practically, you can only generate sine, triangle, and square waves. Modulation is possible, but requires extra hardware to pull off. The advantage I see of the DDS is that, once the signal generation portion of the product is software based, you can push upgrades to functionality via software updates. Not something any XR2206 can do!
aDfbrtVt 6y ago
In theory yes. The issue is the different load conditions will mess with the voltage divider bias. Check out page 272 and onward of the HP33120A manual https://coupp-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=206&filename=hp_33120a.pdf&version=1 https://coupp-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=206&...
- jacquesm 6y ago
  Why compare a commercially available top of the line function generator with a hobby project? At this level you can add a couple of simple components and get 95% of the functionality and accuracy of the commercial one for a couple of bucks. Go higher than that and you might as well shell out the money for an army surplus one, but that does not get you what he wanted: an opportunity to tinker and learn.
  - cushychicken 6y ago
    Why compare a commercially available top of the line function generator with a hobby project? Because as soon as you do, you start to realize that you can get quite a ways with commodity hardware. Hence, why I started this project. The research I've done on the frontend of this on what's available in the market suggests to me that there's a niche for something that's a little cheaper, and a little easier to use. I also have a hunch that portability is a nice feature for most folks as well. (Hi Jacques!)
    - jacquesm 6y ago
      There is a whole branch of Chinese manufactured pc peripherals aimed squarely at this space, digital scopes, spectrum analyzers and so on, don't they make a function generator?
      - cushychicken 6y ago
        They do, but the usability leaves something to be desired.
    - 6y ago

cushychicken 6y ago

Hi! Author here. You are absolutely right, and I called out a lot of those limitations in my original design doc. http://cushychicken.github.io/bfunc-design-doc/ http://cushychicken.github.io/bfunc-design-doc/ I'm just starting to get to work on the second version of this board, and I'm planning on addressing all of these in that design.