are all the function generators gone?

Isn't there a way to generate a sine wave using a Johnson counter and a resistor network?

Ah, check out US4368432 (expired) .. the 4018 chips are still available.

Much easier, cheaper, and more flexible to use a PIC and a DAC.

($1.00)

($2.00)

You can store the sine table in the PIC, and sequence through it at any frequency by using the clock (internal or crystal) and a built-in programmable counter. Easy to synchronize phase. You can also select triangle, square, or any arbitrary waveform you like.

Paul

That should work. I'd switch the clock frequency to make FSK. It should be adequately phase coherent.

--

John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation

If I was going to go and write code, I'd probably spec something more like the ATXMEGA164A4U-MH, which is $1.80 in 25's and has two 12-bit DACs on board, as well as a dozen 12-bit ADC inputs to read the trimpots. Being an agnostic architecture-wise can pay off.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

That is two components from which one is programmable. When using a controller I'd go for PWM and skip the DAC. But then again, a 'discrete' solution might be much simpler.

--
Failure does not prove something is impossible, failure simply 
indicates you are not using the right tools... 
nico@nctdevpuntnl (punt=.) 
--------------------------------------------------------------

Yep. I've even been known to create Gaussian rising and falling edges that way to keep digital modulation schemes clean... as in WiFi.

...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

That's neat, Just remember to factor in the 4018 output impedance.

George H.

Microchip now has a PIC with a DAC (8 bit) on-board:

($1.64/25)

It also has two switch mode controllers, two op-amps, 3 comparators, and

voltage reference. And it has five fully differential 12 bit ADCs. I'd rather stay with what I'm familiar with.

There is almost no reason anymore to design something using discrete components and basic logic ICs.

Paul

The DAC looks like a derivative of their older crude 5-bit DAC-- in fact with (unfortunately) typical uChip datasheet attention to detail, they've copied and pasted parts of Figure 19.1 so it shows a

256-resistor ladder feeding into a 32:1 mux.

One ADC with an option to have 5 differential inputs or 11 single-ended.

There are applications where we need actual multiple ADCs.

There's less reason to do that with most of us using 'C' these days, but my impression is that Atmel is a bit spotty on long-term availability etc. for small scale customers. As typical with newer stuff, that uChip part has some fairly significant errata, much of it relating to the analog-y stuff (but not the DAC)

Some of the stuff they don't get around to fixing for years..

Not big boards filled with logic, but tossing a few logic chips at part of a problem is often a decent way to go, especially with single and dual gate tiny packages. Micros are only one arrow in the quiver.

Microchip's Configurable Logic Cells are interesting- incorporating a few gates or even a logic-level 555-equivalant onto the chip, though I've not yet had occasion to use that functionality.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

On a sunny day (Fri, 14 Dec 2012 22:28:33 -0500) it happened Spehro Pefhany wrote in :

I dunno, but for a function generator just use a FPGA with internal RAM loaded from the PC and any DAC you think suites the purpose. PWM ADC is suited only for very low frequencies.

Somebody here from Germany already did such a project:

from the PC

I suggested using a micro with a real DAC on board, but 125kHz 8-bit PWM should be more than okay for something like Bell 202 AFSK- so one

Nicely done.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

On a sunny day (Sat, 15 Dec 2012 11:10:53 -0500) it happened Spehro Pefhany wrote in :

from the PC

He does really nice projects.

Wow. i am surprised that there are any 2206 or 8038 types left anywhere.

So do you have the specs on that teachscope thing? If it is within my grasp i might try it. I am not really sure what i may be getting myself into here, i could easily hit a hole (more likely a rot spot) in my edumacation.

?-)

George and I had exchanged some discussions about a year ago and he sent me a sample board (they made 12 different units

-- variations on a theme -- but he sent no power supply or casing) to try out. I put some time into thinking about a few things, but other work has taken priority. (Our discussions were without any commitment either way, as I recall it.)

George can speak for himself, obviously. But I think there is an interest, also, in updating the system so that it helps teach users aspects of using both analog and digital scopes. So there are lots of room for suggesting ideas, I suspect.

In any case, if you decide to get moving on something like this I could certainly send you the unit that George sent to me (he may be in short supply.) And if you feel there is anything you may be able to accept, by way of help, I'd be happy to work with you on whatever basis you wanted. My only interest would be in furthering this for George's interest. I'd like to do that, if I can. But otherwise, if all I do is pass along some information then I'd be happy with that role, too.

Let me know.

Jon

s f

Hi Joseph, Well there are no real 'specs'. The idea is a cheap device that spits out different waveforms. Students (moslty physics undergrads, for my market) learn how to use a 'scope by finding all the waveforms. So different time bases, vertical gains, AC and DC coupling, auto and normal triggering.

Hmm, As I'm writing this, I wonder if the 'autoset' button on newer 'scopes makes all this moot? (I never use the auto set button so I've no idea how well it works.)

OK, I dug an old board out of stock, today The autoset button on my TEK found everything but the very slow (few Hz.) waveforms. It'd be nice if the next version of teachscope had a few settings where there were two (or more?) signals at different levels/times. (Now I'm in an 'arms race' with the autoset button?)

I hope I haven't misled you with talk of 1,000 of units. I'd like someone to make/sell thousands so I could ask my customers to buy them (at the tens to a hundred a year rate) We stopped making it because it was too big an expense to get another batch of boxes printed. (We were also getting low on cheap brick on a rope PS's) (Box, PS, switch, connector) As I've said before, the electronics inside is almost free.

George H.

S

ps

lf

Grin, Thanks Jon, my interest is totally selfish, I wish more of my customers knew how to drive a 'scope.

George H.

anywhere.

DDS

a

steps

'signals'

my

myself

Hmmmm. I think i have some beautiful ways to make autoset very challenging, a few modulated signals with the modulation signal appearing elsewhere. And we can produce many more signals easily so long as they do not have to be really high quality of their type. Maybe 30 to 50 signals? Indeed, low quality signals may be more challenging.

+/- 12 and 15 V stuff is getting scarce, maybe we want to change to +/- 5 V analog and 3.3 V logic. As you say packaging and PS are major cost items, let's see what we can do about that.

?-)

If you do move forward on this, I'd appreciate being kept in the loop at some level acceptable to you. I'm very interested if that's okay.

Thanks, Jon

An old (BC, before CAD) design of mine, a little hard to read...

Takes Analog Devices parts, with embellishment, to improve sine wave distortion; and methods to adjust frequency, etc, nicely. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.