Error with schematic in "Robot builders bonanza 2nd. ed." p. 287?

There is no error in the schematic, though half of the JK flip flop chip is labelled 7576 rather than 7476--there is no such chip with that number. If you review the way the circuit works (XOR logic), it is not possible to have it work in one direction and not in the other when you change the polarity of pin 12. Connect LEDs (with suitable current-limiting resistors of course) to the outputs instead of the motor, and you can better see the stepping sequence.

This is a very common schematic since the first edition of RBB in 1987, and has been replicated countless times in other books and on the Internet. Dennis Clark also has the same schematic in his book Building Robot Drive Trains, though his shows pin 14 for one of the inputs of the

7486. That is easily correctable by looking at the pinout for the 7486, which shows pin 14 as Vcc (note that pin *13* is Vcc on the 7476, which is unusual--be careful with this one or your circuit won't work).

More than likely the stepper coils are not connected properly to the four outputs of the flip flops, you aren't using a unipolar motor, and/or there is a wiring error in your circuit.

All known issues with the book can be found in the errata on

-- Gordon Author: Constructing Robot Bases, Robot Builder's Sourcebook, Robot Builder's Bonanza

Sorry, there *is* an error. Just caught it when I double-checked the pinout. Pins 13 and 5 of the 7476 are reversed -- pin 5 is Vcc and pin

13 is ground. Got bit by the same bug I tried to warn you about.

I've updated the errata to include this. Thanks for leading me to it.

-- Gordon Author: Constructing Robot Bases, Robot Builder's Sourcebook, Robot Builder's Bonanza

Hi! Yes it works. Seems likte it draws more current in the other dierction. So, I'll just have to change some resistors i guess.. Thanks for the reply, and btw, it is a good book...gets me inspired :)

--Anders Folkess> Gord>> (note that pin *13* is Vcc on the 7476, which