Maplin Function generator PCB kit.

[bikerhifinut]

Thought I would share this with you all.
I bought one of the pcb based kits from maplins that makes a function generator, using a dedicated? IC plus an op amp and a LM358 for a speaker output.
They allege it produces a 5 volt output, adjustable frequency (but not what range) and selectable sine, square, saw and triangle waveforms.
I got it to use with a Phillips CRO that I was given.
it cost as I remember about £17, and works from 12Vdc.
Well................ I have either ******** something up on the board which I don't think I have, or its basically a heap of garbage. The waveforms are all hopelessly distorted, of no use whatsoever in a diagnostic role and the output voltage leaves a lot to be desired and varies across what limited frequency range it seems to have.
Not recommended.
There's no circuit diagram supplied with the kit, and no real technical info.
The generator chip is a ATTINY2313 if that means anything to anyone.
I powered it from a 12V leisure battery so I dont think PSU pollution could be a cause of the nasty waveforms. The chips all fit in sockets so no worries about heat/static damage from the iron. And yes I did check i put them in the right way round!
Not impressed.



Andy.

[bikerhifinut]

Fortunately I have a fully working Levell signal generator with a continuously variable 3Hz to 300KHz range over 5 ranges and a variable output sine and square wave. And the waveforms look good on the scope. So I know the scope is ok. I took it to Ed Dinnings for a onceover so I am sure its good enough.

Andy.

[TonyDuell]

The ATTINY is a (programmed) microcontroller. IIRC this kit is that chip + a resistor DAC and not much else. I built one, and estimated the circuit by looking at the PCB.

Like you, I found it totally useless. A wien bridge oscillator works a lot better.

That series of kits, which seem to come from some company associated with Middlesex University claim to be 'educational'. Since none of them that I have come across come with schematics or any form of theory of operation I can't find any educational value in them. A total wase of money.

[bikerhifinut]

Couldn't agree with you more Tony. Some of the kits were ok but this latest range aint. I got it as an aid to getting my head round using the 'scope which is why the saw tooth function would have been fun to play with.
We live and learn.

Andy.

[bikerhifinut]

Tried the website on the wrapper. It put me through to Maine University in the USA!
Looks like they have had an issue with website domain names as I found they now call themselves Mindsets Online.

[Restoration73]

Whilst I agree it is not as educational as earlier kits using the 8038 waveform
generator ic, as it tunes in steps, and the frequency response of the speaker output
has a limited frequency range, my one worked OK. The data is on the Maplin site
https://maplindownloads.s3-eu-west-1...n42fl-6612.pdf

[Ed_Dinning]

Hi Andy, see if you can get an 8083 from the web, I don't think they are much and I'll give you the circuit for a good generator (it was in PW or PE many years ago)

Ed

[Radio Wrangler]

Well, it certainly looks like it's being educational.

There are several sorts of signal generating instruments out there:

1) LC oscillator - these usually appear as RF signal generators. Switched inductors are resonated with a variable capacitor and tune from several tens of kHz to maybe 100MHz or so. Expect an AM modulator and maybe a little audio oscillator to make some modulation. Posh ones will have extensive screening and wide range calibrated output attenuators. Makes a very pure sinewave

2) Frequency Synthesisers various models covering audio up to microwaves, sometimes with RF signal generator style modulation and attenuators. internally they are LC oscillators with digital frequency control and correction. Newish ones are very expensive, oldish ones are heavy on maintenance demands. Usually makes quite a pure sinewave.

3) Wien Bridge Oscillator - an RC oscillator, good for 10Hz to sometimes 10MHz. Moderate stability. Fairly low noise. Excellent for low distortion audio work.

4) Analogue Function Generator - a very general purpose voltage controlled waveform generator which can include ability to make multiple waveshapes and to do sweeps. The internal circuit is a voltage to frequency triangle generator. Diode shaping is used to bend this into an approximate sine wave. Squaring makes a squarewave. Only really useful for general bench work rather than for serious use. Some cover 0.001Hz to 20MHz. Poor harmonic performance, not very clean, not very stable. Usually cheap. There was an analogue chip that integrated a whole func generator ("8083").

4) Digital Function generator or 'ARB' - a microcomputer or a specialised DSP processor can be programmed to send data to a DAC which will make all sorts of waveshapes and frequencies. Not only sines, squares, triangles and ramps but you can on some enter your own arbitrarily chosen shapes (hence ARB) Some of these are quite good, some cheapies are total junk. All run into trouble when running dfast enough that there aren't many samples in a wave. Stable, can be dirty to reasonable at best, some give very erratic results.

I think you've run into a bad example of (4) and they aren't a substitute for a decent Wien Bridge oscillator.

David

[TonyDuell]

A variation on [1] : A pair of (RF) LC oscillators mixed together and the difference frequency is fed to the output. Until the development of the Wien bridge oscillator this was the main way to get an adjustable audio signal generator. It was something of a touchy instrument, if you got the 2 oscillators close together in frequency to get a low frequency output it was not uncommon for them to 'jump into lock' and the output to fall to 0.

I remember building both that design and a Wien bridge oscillator using the excellent Philips EE kits some 40 years ago. Now those really were educational.

I got one of these http://www.ebay.co.uk/itm/new-DDS-Fu...-/181882407616 works quite well, and you get a circuit diagram. It was worth the tenner for the display alone, mine came from China with postage included. Great fun to build, great fun to plug into an oscilloscope, not much real use though. Thought about putting it in a box with a 'speaker as an audio tone generator, nice idea but I bet the battery shelf life would be the limiting factor.

[David G4EBT]

I appreciate that the title of the thread relate to the Maplin kit and your dissatisfaction with it, but f you're just looking for a simple sine/square/triangular waveform generator to use with your scope Andy, I'm not sure what benefits - if any - a PIC-based generator confers over the well tried 8038 chip, which has been around for decades but refuses to die.

There are lots of 8038-based kits and ready made modules around costing under a fiver. Depending on what one wishes to do with them, they may need some refinement, such as a switch to select various frequency ranges rather than a jumper, or if it's desired to box it up, normal front panel pots in place of on-board pre-set sub-min pots, but that's really no big deal.

To give just a couple of examples:

1) "ICL8038 Function Signal Generator Module Sine Square Triangle Wave Output". In kit form, it ranges from 50Hz – 5kHz, sine, square, triangle waveform. £4.30 post free.

2) A ready built board described as: "10HZ~300kHz ICL8038 DDS Signal Generator Module Sine Square Triangle Wave" has the following features and costs £5.30 post free:

(1) output triangular wave, square wave and sine wave.
(2) frequency range: 10HZ ~ 300kHz
(3) Duty range: 2% to 98%
(4) Low-distortion sine wave: 1%
(5) low temperature drift: 50ppm / ℃
(6) of the triangular wave output linearity: 0.1%
(7) Power supply: + 12V ~ + 24V

I won't quote the ebay links for these two examples, but these and lots of other kits and ready-built 8038-based modules abound and are easy to find. Of course, if the object of the exercise is to learn what can be done with PICs, rather than to simply acquire a low cost basic waveform generator with adjustable frequency & amplitude to use with your scope, these examples won't fulfil that objective.

Hope these observations are of interest.

[TonyDuell]

Originally Posted by David G4EBT

Of course, if the object of the exercise is to learn what can be done with PICs, rather than to simply acquire a low cost basic waveform generator with adjustable frequency & amplitude to use with your scope, these examples won't fulfil that objective.

And nor will the Maplin kit that started this thread (no, I am not distinguishing between PIC and ATTINY). That kit comes with a pre-programmed chip, you do not get the source code, or any idea as to how it works. I think it's copy-protected so you can't dump out the code and disassemble it.

[bikerhifinut]

Originally Posted by Ed_Dinning

Hi Andy, see if you can get an 8083 from the web, I don't think they are much and I'll give you the circuit for a good generator (it was in PW or PE many years ago)

will do Ed

Andy

[bikerhifinut]

Thanks guys and a very stimulating set of responses.
I was mainly making a comment on my experience, and of course not having the depth of knowledge of most of you gents (and ladies) I learned the hard way.
I have a fairly decent if old "Levell" signal generator which generates a good sine and square wave so I wont be left with nothing.
The 8083 route sounds interesting. Thanks Ed and the others.
I will eventually hope to use the scope as a fault finding and setup tool for my various valve audio projects and that was the reason for getting the sig gens.

Much thanks.

Andy.

[TonyDuell]

I am sure I speak for many, if not all, here when I say that the reason they have a 'depth of knowledge' and I have a little knowledge is that we learnt the hard way too. I at least have made more mistakes than I care to remember over the years....

I remember something said to me by one of the well-known names in electronics : 'The designer who never blew a chip is a bad designer. He never designed anything'.

...blew a chip is a bad designer. He never designed anything'

Or more like, never built anything. That's why I like (good) kits, they make you know it can be done by your own hands. After a bit your own designs will be built, corrected, re-corrected and then be working. Big smiles all round.

[mhennessy]

The thing is, the ICL8038 was discontinued a while back: https://en.wikipedia.org/wiki/8038_ic

So what exactly are these "new" ICL8038 kits using?

This reminds me of a recent conversation about the TDA2030. Are these ICs NOS, or are they being second-sourced? Are they any good compared to the original Intersil and Maxim versions?

I presume the mention of "DDS" in the description that David alluded to in post #11 is "clickbait"? I had a look at the listing, and it certainly isn't DDS. Hmm...

Making a triangle+square wave oscillator is just 2 op-amps (an integrator and a comparator). Turning that into a sort-of sine wave with a bunch of diodes would need some experimentation, but it's eminently doable. A couple of hours with a breadboard, a couple of PP3 batteries and a 'scope would be time well spent - far more educational than that kit.

Unless the kit is intended to teach microcontroller principles, I suppose. Do they supply source code and suggestions for modifications? If so, that's probably quite good. But I'm guessing not?

[bikerhifinut]

you get a pcb, a parts list and the parts. No circuit diagram. and some basic instructions.
Anyway it was an afternoon spent finding out what a rubbish waveform looks like.

[Radio Wrangler]

Yeah, educational!

An American friend has a bit of a sense of humour. He liked to salt presentation slides with some unexpected ones. I particularly liked:

"Experience is what you got when you didn't get what you wanted"

But his best one was:

"If the opposite of pro-something

is con-something

Then the opposite of progress must be ,..........."


David

[Wendymott]

A few years ago I worked in the returns dept of Maplins at Wombwell S Yorks. I used to evaluate and repair returns. My fields of interest included Scopes and the Electronic kits available at that time "late 90's". One of the recurring returns was the Function Generator. This had been designed around a dedicated Function generator chip, sorry I cannot remember the device type maybe the ICL8083, and a few CMOS Nand gates. It was obvious to me that the Nand gates were causing a "Race" condition, that meant logic pulses were appearing before required and caused "latch up". This was caused by the chips supplied being NOT what was in the original design. i.e possibly designed with Texas, and supplied with RCA. I offered to re design using a PIC and the function chip, IN MY OWN TIME, but this was dismissed, tooling costs etc being prohibitive for the small amount of kits sold.
In the early days of Maplin, they had a great Ethos, reasonable components and kits at reasonable prices. However as with "Topsy" it grew to today where some items leave a lot to be desired.
I had a great time there, "18 months" repairing all sorts, from Scopes, TV cameras, Radio controlled toys but while I was there they closed the entire New products Evaluation dept. Bean Counters.... Grrrrrrrrrrrrrrr