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Farm Machinery
Precision Farming & GPS
Berthoud/Trimble speed signal
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<blockquote data-quote="Pheasant Surprise" data-source="post: 4387730" data-attributes="member: 1103"><p>A “genuine” radar output will be switching between 0 and 12 volts on the output speed pulses. It would apppear that the EZ250 only switches it’s simulated radar output between 0v and 3v ~ 5v or thereabouts. So on some boxes that lower threshold voltage may work....and on others it will be too low to reliably trigger the input.</p><p></p><p>The pull up resistor works by tieing the radar input pin to 12v, then when the 250 pulls its radar output pulse low, it pulls that input pin down to 0v so you get the “full” 12v for the pulse change - so it triggers correctly. The pull up resistor stops too much current getting drawn/sunk from these I/O supply pins including the EZ250.</p><p></p><p>I’d say the EZ250 probably has got clamping diodes built into the I/O of the unit. An extra external diode in series will reduce the little output voltage from the pin, so any benefit may actually be a hindrance.</p></blockquote><p></p>
[QUOTE="Pheasant Surprise, post: 4387730, member: 1103"] A “genuine” radar output will be switching between 0 and 12 volts on the output speed pulses. It would apppear that the EZ250 only switches it’s simulated radar output between 0v and 3v ~ 5v or thereabouts. So on some boxes that lower threshold voltage may work....and on others it will be too low to reliably trigger the input. The pull up resistor works by tieing the radar input pin to 12v, then when the 250 pulls its radar output pulse low, it pulls that input pin down to 0v so you get the “full” 12v for the pulse change - so it triggers correctly. The pull up resistor stops too much current getting drawn/sunk from these I/O supply pins including the EZ250. I’d say the EZ250 probably has got clamping diodes built into the I/O of the unit. An extra external diode in series will reduce the little output voltage from the pin, so any benefit may actually be a hindrance. [/QUOTE]
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Farm Machinery
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Berthoud/Trimble speed signal
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