Dr Bob Beck uses a 555 timer to a transistor which switches the relay on and off. The relay is cross-connected and all the circuit actually does is swap the output from a 27 volt battery source. i.e The battery plus is connected to A and the Minus to B.
When the 555 output goes low the relay drops out and the battery plus is then connected to B and the minus to A
In other words if a motor is connected it will turn forward and then reverse, that is the same function as an H-Bridge.
The H-Bridge I came across has two inputs. a totem pnp/npn transistor configuration on the left and the same circuit on the right.
My question is if I remove the switching transistor and the relay how do I connect, probably using two transistor to replace the 74HC14's (A and B) or direct to the1K resistors, to switch the H-Bridge on and off thus reversing the output. The output load is 30 to 100 micro-amperes so small transistors will do.
Sorry Pete I battle with attachments.