Mini-Mod 2021!

[Pamphonica]

Hi Peter, I have used one of your Mk1 boards - very nice!
Would it be worthwhile making those transistor pads yet further apart by quite a bit? They are still quite cramped for some people to solder successfully.
All best
Jeremy

[Electronpusher0]

Hello Jeremy, I will have to make my own footprint for the transistors, the ones on the draft board are the largest in the library and designed for hand soldering.
Making your own footprints is quite easy, that's what I did for the inductors as there is no standard footprint for toko coils in the standard library.

Peter

[Electronpusher0]

OK, I have made my own footprint for the transistors to make soldering easier.

New draft layouts attached (I have changed the front copper to green just for illustration)
Also detail of the transistor pads.

Any other suggestions / requests are welcome.

Peter

[Pamphonica]

Wow - thats a quick turnaround for a re-layout! I think that those larger pads will help.
many thanks
Jeremy

[Electronpusher0]

Having got my head round KiCad I am surprised at how easy it is to update and change an existing layout. It's certainly worth the effort of learning.

I have given up breadboarding on vero except for the simplest of circuits. It's just as easy to lay it out in KiCad and order the boards from JLCPCB, it looks much proffesional and I always manage to build in errors with vero.

Peter

[Electronpusher0]

I looked again at what would be a useful addition and decided to add a 3.5mm jack socket for the audio input.
I decided to use the PJ320A which seems to be readily available from Amazon, e-bay, aliexpress etc.
I purchased 15 for £5.49:

https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1

I had to create the footprint though.

Images of the front and back attached

Peter

[Electronpusher0]

Hopefully this is the final version of the MK2 Minimod.
Ian has now finalised the design with the added buffer stage.
I have added the features described above and I have also added a 78L09 regulator, diode and capacitors for those who wish to use an external power supply.
The components for this are numbered from 100 to distiguish them from Ian's design

For battery use, or if you do not want to use the regulator, simply omit the regulator and replace D101 with a link. The extra capacitors do no harm and can be fitted if you wish.

I have still kept the pcb size the same to allow it to be easily fitted in place of the Mk1 board for those who want to compare the versions.

I will leave it for a few days for any other comments / requests before ordering the pcbs.

Peter

[bikerhifinut]

Lovely job!
I just wondered if it would be an idea to rework the Voltage regulator to incorporate a standard adjustable regulator. that would of course entail squeezing in a couple of resistors for the potential divider network.
I figured theres a fair few of us with a drawer full of LM317/LD1084 etc etc 3 legged regulator chips which can be used for any voltage between about 3 to 30V.
But that really is a nit pick and I'm very impressed and not a little envious of your command of KiCad which I could not master at all.
Best regards.
Andy

[Bazz4CQJ]

I too am in awe of your command of Kicad. Have you thought about running one-day tuition courses?

B

[TopOfChassis]

I'm looking forward to the PCBs being finalised and produced, I'd certainly like a couple. I've already sourced the inductors and transistors in anticipation (the rest I have in stock).
Thanks for your efforts.

[Electronpusher0]

Originally Posted by bikerhifinut

Lovely job!
I just wondered if it would be an idea to rework the Voltage regulator to incorporate a standard adjustable regulator. that would of course entail squeezing in a couple of resistors for the potential divider network.
I figured theres a fair few of us with a drawer full of LM317/LD1084 etc etc 3 legged regulator chips which can be used for any voltage between about 3 to 30V.
But that really is a nit pick and I'm very impressed and not a little envious of your command of KiCad which I could not master at all.
Best regards.
Andy

Interesting thought, I did hesitate about the 78L09 as it is not as readily available as the 5V and 12V versions.
I will take a look at what I can do.

Peter

[Electronpusher0]

Originally Posted by Bazz4CQJ

I too am in awe of your command of Kicad. Have you thought about running one-day tuition courses?

B

Thank you Bazz, as I said, learning KiCad was a lockdown project. I will give the idea of tuition somee thought.

Peter

[Electronpusher0]

Originally Posted by bikerhifinut

Lovely job!
I just wondered if it would be an idea to rework the Voltage regulator to incorporate a standard adjustable regulator. that would of course entail squeezing in a couple of resistors for the potential divider network.
I figured theres a fair few of us with a drawer full of LM317/LD1084 etc etc 3 legged regulator chips which can be used for any voltage between about 3 to 30V.
Best regards.
Andy

Well I have taken up Andy's challenge.
I created a custom symbol to represent the regulator so that either a 78LXX device or an LM 317 can be used. I also created a custom hybrid footprint so that again either device can be inserted.
R101 and R102 are the voltage programing resistors, the present values give 9.6V which is about what a new 9V battery gives. (although if using a 12V walwart you might want to reduce this to give the specified 3V headroom for the regulator)
R101 and R102 are not used if using a 78L09.
Again if using battery then U101 is not fitted and D101 replaced with a link (R101 and R102 are not used in this case also)

Again I will leave it a couple of days for final comments and then order the pcbs.

Peter

ps the detail view of the regulator footprint is looking from the top without the groundplane and showing the rear tracks as though the board was transparent

[bikerhifinut]

That's fantastic!

I think if you use an LDO regulator rather than the good old LM317 you'll get away with nearer 1.5V voltage drop if pushed.

I'm more than impressed. And the Minimod is a jolly useful circuit.

Andy

[Ambientnoise]

Isn’t the circuit around the 317 wrong ? I think the voltage set resistor should go to the output not input.

[Electronpusher0]

Originally Posted by Ambientnoise

Isn’t the circuit around the 317 wrong ? I think the voltage set resistor should go to the output not input.

Yes you are right, thanks. I was thinking the flow was left to right.
That's why I put it on the forum before ordering the pcbs.

I'll correct it.

Peter

[Electronpusher0]

I have corrected the error spotted by Ambientnoise. Corrected schematic and pcbs attached.
I will now order the boards, I will order 30 initially, I am really not sure how much interest there will be.
When they arrive I will build a couple, one with 78L09 and one with LM317.
When I am completely happy I will offer the rest of the boards on the correct part of the forum.

Peter

[David G4EBT]

Great improvements to an already excellent PCB by modifying the pads for an input socket, and the transistor pads to make soldering easier. It's remarkable that with Peter's efforts, the original Mini-Mod designed by Ian, G4JQT all those years ago, continues to be very much alive and kicking. Also, it great that due to its popularity, Tony Nailer of Spectrum Comms has put together a component kit.

Without wishing to sound in any way critical, I'm wondering why the inclusion of a 9V voltage regulator, when at best a new 9V battery voltage will be about 9.5V or so? Most voltage regulators need a minimum input/output voltage differential ('dropout voltage') of at least 2 volts or so, or the regulator has too small a differential voltage to regulate. The 78L09 datasheet spec says that the input voltage can be from a minimum of 11.4V to maximum of 24V and that (at 40 mA) the output voltage will be: Min 8.64V, typically 9V, Max 9.36V.

See page 6 of the datasheet, under 7.6:

https://www.ti.com/lit/ds/symlink/lm78l.pdf

Apart from the fact that the LM317 is a 1.5A regulator, (why 1.5A for a mini-mod, when a 0.1A 78L09 would be more than ample?), its dropout Voltage is stated as 2000 mA (2 Volts), so again, with an input output voltage differential of only 0.5V or so, even with a fresh battery, it has nothing to regulate:

https://www.ti.com/product/LM317?utm...B&gclsrc=aw.ds

Different of course if say the Mini-Mod were to run on 5V and used a 79L05 regulator, which would continue to provide 5V out until the input Voltage from a 9V battery dropped to 7V or so.

I haven't read every post so I might have missed something which answers this query.

Every success to those who build the latest version.

It's been so popular that I though by now, everyone has got at least one - I've got two!

My daughter-in-law says 'you can't have too many pairs of shoes or handbags'.

Maybe the same could be said of mini mods.

[Electronpusher0]

Hello David, to answer your comments.

It is never intended that the regulator be used with a battery, for battery use the regulator is omitted and D101 replaced with a link.

The regulator option was added for those (like myself) who want to use an external (mains) power supply.
Initially the regulator was just the 78L09 but in response to a request from BikerHiFiNut (Andy) (see post 108) I made the regulator pad dual purpose to take either a 78L09 OR an LM317 (with the addition of R101 & R102).

I wanted to make the power options as flexible as possible.

Regards
Peter

[David G4EBT]

Thanks for reading my query Peter and for your response, which explains the rationale for including the regulator.

You've certainly got to grips with Kicad!

The number of posts in this thread (119 to date), and the number of views (almost 14,500), is testament to the ongoing popularity of the Minimod.

Long may it continue.