Quote:
Originally Posted by Hugh Meyer
It seems noise into the Jaguars is causing the reset issue mentioned here and in another thread. When one connects an encoder or other circuit to the encoder input it works as an antenna to pick up noise.
So far I have found a 25 uf cap across the + 5 volt pin and the gnd pin on the encoder connector fixes it.
This may not work if all ground loop issues are not resolved. The opto isolators are needed to remove the ground loops and the filter cap is needed to filter the spikes created by the back emf when the motors stop or change direction.
We are using shielded wire with the shield grounded at the Jaguar and open at the custom circuit board where the opto isolators are located.
The only connections back to the Jaguars are from the output transistor in the opto isolator. I have seen some high frequency roll off and trouble with phase shift causing direction changes. I am still working this issue. If the noise is really fixed I might try to add another pull-up on the opto board to the +5 volts from the Jaguar.
Has anyone else seen these issues?
-Hugh
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The board we used didn't drive the transistor into the Jaguars. It drove the inputs of the Jaguar with the outputs of the 74HC04 inverters the Jaguars themselves were basically powering (instead of the encoders). The inputs to the 74HC04 inverters were in turn connected to the NPN transistors pulled up with 4.7k - 6.8k resistors. Under other circumstances 4.7k would still leave enough margin to drive older 7400 series inputs.
To deal with the power supply issue for this circuit:
Initially we used a 7805 connected to the battery with a 4,700uF electrolytic capacitor on the input with a 10uF electrolytic and 0.022uF poly capacitor on the output. I'm almost positive we aren't allowed to do this on the robot. So we then started taking our power from the digital side car for the encoder side of the circuit.
Basically both our encoders, and the logic driving the optocoupler diodes, was powered by the digital side car with a small capacitor. As a matter of practice I'd be pretty concerned if that capacitor on the digital side car got too big as the inrush could have consequences.
I am still making efforts to provide these schematics. I'm sorry about the delay I'm extremely pressed for time lately.
I'm going to push to finish this up tonight...but no promises I haven't slept in some time.