Dual NPN, 40V-Is it ok to use MMDT3904-7-F instead of this MMDT3904-TP

I want to know about replacement ofDual NPN transistor, 40V
Is it ok to use MMDT3904-7-F instead of this MMDT3904-TP

Looks like the datasheets match up and they both belong to the same 3904 family. So its safe to say you could use either.


  1. Hello Mohit, Thanks a lot for reply. I was worrying little about the footprint of MMDT3904-7-F, is it compatible? As we have already order PCB fab from OSH Park.

  2. I guess, (from your name) you are from Indian Origin…! :smile:

By the way, I’m professor at Engineering College in Pune, India.
We are team of three people working on latest Software and Hardware technologies to bring up some innovative product for Common use. We are working on one such project which is inspired from spark, Arduino style compact systems…!

That sounds great!

The footprint is SOT-363 in both the cases, so that should not be a problem.

Please keep us updated on your progress!

Hi @mohit,
For 32khz crystal capacitance, therer 2 options
your BoM says the crystal cap shud b 7 pf
but available cap is 9pf and 12.5 pf
which one wud b better… 9pf or 12.5 pf ?

Also… we got the chip antenna in kns is hving freq range 2.4 to 2.5 Ghz
bom’s chip antena hving freq range as 2.3 to 2.7 Ghz. is it ok!

STM32 datasheet recommends RTC crystal with a load capacitance of 7pF or lower. Try finding other options as 9pF or 12.5pF won’t work.

Antenna is a tricky business. For the given values of the LC network, we highly recommend the mentioned antenna. Other antennas will still work but at the expense of poor RF performance. You could also try using an external antenna if a chip antenna is hard to find.


Hello @mohit , the bom suggests the diode of 30 V 3 A , Vishay make. The diode has DO220AA which is SMP footprint. We find an alternative of Vishay diode rated as 20 V 2A, DO220AA footprint. Will it work ? please suggest

Thanks a lot @mohit!!
We have now found almost all components and their alternatives…!
Its very dificult here in india to get tgese component. we are really struggled a lot
to gather all these component.!!!

  • Only components left is diode SS3P3-M3/84A…! is there any suggestion frm your side.
    as also posted by my partner @GauravB

Rajendra :smile:

Yes, that should work as well!

That’s amazing! Having grown up in Mumbai, I know the struggle of finding the right components easily even though China is right next door. You could try online vendors like element14/Farnell/kitsnspare if something cannot be procured from Lamington Road.


Thanks for the reply @mohit

We have found almost all components from KitsnSpares except LEDs and Header. We decided to buy diode of 40V, 2A rating, Vishay make, DO220AA foot print as it was in stock. Hope this diode too would work fine. The antenna we decide to buy from a China vendor. So all would be in place in coming 2 weeks and we soon gonna start building our first Spark Core

Thanks and Regards
Gaurav :slight_smile:

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Hey @mohit great to here you r frm Mumbai…! We are planing to go Mumbai tomrow… :smile:
We got almost 90% of component frm KnS, with few alternatives…! Some we have got as sample.
Like Wifi chip, Buffer and SPI flash… so its going good…!

@bkrajendra How is the Core coming along?!

Hi @mohit, actually we are waiting for PCB from OSH park. We have also having contact with local indian PCB fabricator in Gujrat (www.pcbpower.com). The main pain was getting component. We found almost all, but purchasing them was real job. as initially we need less quantity, its difficult job…! We just had talk with Element14 Bangalore. lets see what offer they have for us…!
We’ll let you know as soon as we make some considerable progress!!

Dear @mohit,
We are in the phase of making PCB. The Indian PCB fabricator PowerPCB we’ve selected for it. But the problem they are facing is with MicroUSB 0.5mm slot. They have 1.0mm slots only. We tried editing eagle library or board, but it changes the pad size. Can you suggest us any alternative.!

An alternative will be to change the slot to a hole or use a USB connector with SMT anchor pads (no slots).

Something like this: https://www.sparkfun.com/products/8533

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