Blood Machine Project

[Renier]

Hi guys & gals

I'm fairly new to the hobby electronics field, so please bare with me. I'm planning to build a blood machine for our Veterinary practice. I want to insert an unstained blood slide on one side and have it dried (12V <1A PC fan), stained (4 different stains squirted with 5V <0.5A DC motors) and moved to and fro (2x stepper motors 15V 0.4A) between these components. I'm planning on using an Arduino uno (12V 1A) with 2 darlington arrays (stepper motors) and 5 Transistors (fan and 4x DC motors). Obviously each component will work one at a time. I've done the basic drawings, but being new, I'm quite unsure how it will all incorporate. I plan to use one 15V 3A DC adapter to power it all, but I'm unsure if the idea will work with parallel circuits and intermittent components (controlled by the arrays and transistors). How will I approach this problem? From some experience, might it work with only one circuit or will I have to separate the components w.r.t power sources.

Any ideas or guidance please.

Thanks