Steppers and the SAA1027.

[cactusface]

Hi All,
I have just got myself a couple of nice 200 step stepper motors and want to put them to use. I also have a couple of the old Philips SAA1027 drivers, whcih as some of the older members may recall makes the job fairly easy, in that there are only 2 inputs Step-in and mode(Drection). The SAA1027 needs 12v+ (or more) no problem as the motors are 12v, but the problem is the inputs are not your normal logic or TTL/CMOS, they requre an HIGH of at least 7.5v and a low of 4.5v max. I did think of using transistors, BUT what about a ULN2003 which would also run at 12v using pull ups, as per the schematic below. I did think of adding an LED between the pullup and Gnd as a visual indicator??

I am open to comments good or bad, ideas or would a L293D be just as good perhaps but needs a full port to drive 2, this is only 4 bits for 2.

Regards
Mel.

 

[westaust55]

Both the transistor and ULN2003 methods should work. The ULN2003 includes 2k7 resistors onto the Darlington bases thus reducing the component count further.

The indicating LED from the pull-up resistor to ground will prevent operation as the LED will give a forward volt drop of the order of 2 to 3.5 Volts preventing the SAA1027 inputs reaching the desired/required voltage.

 

[cactusface]

Hi westy,
Thanks for your reply. I'm go with the ULN2003 as it's neater and keeps the component count down a bit. Funny how things change and you don't notice, I recall LEDs dropping about 1.7V and needing 20mA+, but I used one lately and on 5V and with 820R it was still too bright really just for a power indicator, that's a lot less current. Just tried a test set up and it seems to work OK.

Regards
Mel.

 

[Buzby]

... but I used one lately and on 5V and with 820R it was still too bright really ...

I use 5v and 4.7K for red LEDs on my breadboard, and they are plenty bright enough for that kind of usage.

The efficiency of modern LEDs is amazing !.