signal generator - 2nd generation

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This last week I are mostly doing......

Finally getting round to putting together the original signal generator replacement.

The original attempt: http://www.vitalstates.org/diy/amplifie ... siggen.htm

I’ve seen the light and abandoned the hair shirt methods of native atmel chips and assembler and embraced the luxury of arduino and it’s comprehensive C++ libraries.

I’m in the process of mapping out a pcb, but in the meantime here is the barebones without the opamp buffer stage:
1k sin

1k square

10k square

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and the distortion:

1k

10k

these are much as expected, not quite as good as the wien bridge, but I'm sure fit for purpose.
I will obviously do the measurements again with the buffer in circuit.

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the circuit so far....I've discovered with designspark there is no need to draw a schematic and then convert to pcb layout...it's possible just to draw the pcb layout to begin with:

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an alternative. Uses an 18v 2a wall wart to dispense with the transformer, bridge and 2 x 9v voltage regs. All I have to do now is make up my mind which one. Any suggestions that might sway the decision?

[Mike H]

Have you bread-boarded the new PSU idea to prove it works? With the loads it will 'see'. (Can be 'dummy loads', resistors.) Before getting too deep into PCB design. Guess how I know!

I looked up e.g. 3904 datasheet – hFE seems a mite low for my liking. But might be OK. Only one way to find out! Bear in mind hFE falls as Ic increases, in other words, the more you want it to turn on, the less gain it's got – and you should design for the minimum hFE it says on the datasheet – again, guess how I know ...

[Nick]

How about this using a LM380?

https://makingcircuits.com/blog/simple- ... enter-tap/

[ed]

Have you bread-boarded the new PSU idea to prove it works? With the loads it will 'see'. (Can be 'dummy loads', resistors.) Before getting too deep into PCB design. Guess how I know!

I looked up e.g. 3904 datasheet – hFE seems a mite low for my liking. But might be OK. Only one way to find out! Bear in mind hFE falls as Ic increases, in other words, the more you want it to turn on, the less gain it's got – and you should design for the minimum hFE it says on the datasheet – again, guess how I know ...

I haven't breadboarded the power side yet but I did do the spice thing down to 18R, i.e 0.5 amps without any drop showing. I started at 36R(0.25A) but thought I'd stretch it. If the whole thing takes more than 100ma I will be surprised.

I will deffo live test it before sending the pcb order off, but I don't have an 18v wall wart at the mo so it's on hold at the moment.

@Nick...thanks for the alternative. I must confess I don't fully understand how the circuit works in the first place(yet) so comparisons are beyond me at the moment. I must point out that I have zillions of 39xx and diodes in the box so it enticed me down this route.

[Mike H]

I haven't breadboarded the power side yet but I did do the spice thing down to 18R, i.e 0.5 amps without any drop showing. I started at 36R(0.25A) but thought I'd stretch it. If the whole thing takes more than 100ma I will be surprised.

Fairy nuff!

[Nick]

I haven't breadboarded the power side yet but I did do the spice thing down to 18R, i.e 0.5 amps without any drop showing. I started at 36R(0.25A) but thought I'd stretch it. If the whole thing takes more than 100ma I will be surprised.

Fairy nuff!

Was thinking about the worst case, I guess that is when you need a DC offset on the output signal or a non symmetric wave.