[sdiy] Negative-going triggers in the Boss DR-110 drum machine - Why?

[Gordonjcp]

On Fri, Sep 29, 2023 at 02:34:46PM +0100, Tom Wiltshire wrote:
> 
> You all seem to agree that it's down to the feeble output power of the processors ports, which makes PNP transistors a better bet, and that necessitates the negative-going pulses.
> 
> On a modern processor with much more powerful outputs we could presumably (I'll have to check the currents) drop the PNPs too and use positive triggers, saving even a few more parts.
> 
> Many thanks!

Maybe not! Even modern MCUs have fairly limited current capacity. Something like an STM32F40x can source or sink 25mA per pin (or something in that region, I don't have the data book handy) but a maximum of something like 100mA per package.

The PNP transistors used in the DR110 have an Ic of 200mA which is a spanner dropped across a car battery by comparison.

-- 
Gordonjcp