ping proto board question

jonduncan

could I connect· the ping to the servo location like on the BOE board and still use two servos do i need a 470 om between ping and prop? what is the difference between Vin and 5 v? and would my robot move slower if it is set to 5V instead of Vin?

Mike Green

You do need a protective series resistor between the PING and the Propeller pin because the PING is a 5V device.

The servos operate on 4.8V to about 7.2V. It's better to run the servos off Vin as long as it's 7.2V or less since they can draw an ampere or more and most regulators can't put out that much (particularly without a significant heatsink).

parts-man73

Is there a happy medium resistor value that would work well with both the PING and a servo? Since the resistor would be soldered in place on the Protoboard, it'd be nice to set it up to be able to plug in either.

If I understand correctly, a 4.7K resistor is suggested for a Servo, and a 470 ohm is suggested for a PING.

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Brian Meade

"They who dream by day are cognizant of many things which escape those who dream only by night" - Edgar Poe

Mike Green

I set up the servo connectors on my own Protoboard with 1K resistors and use one position for a PING. The main reason for these resistors is to protect the Propeller I/O pins from excess current if something is misconnected (say to +5V). For the PING, it provides a +5V pulse at times. A 1K resistor limits the current through the protective diodes to (5V - 3.9V) / 1K = about 1ma. If a servo failed and put its supply voltage on the control pin, this would also protect the Propeller. If the Propeller program were buggy and tried to drive the PING pin LOW when the PING was trying to drive it HIGH, you'd still be safe at (5V - 0V) / 1K = 5ma.

parts-man73

Excellent, Thanks Mike!

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Brian Meade

"They who dream by day are cognizant of many things which escape those who dream only by night" - Edgar Poe