harp-tech
Harp Behavior Board digital output to OneBox #170
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A user is using a Harp Behavior Board to send a TTL to a digital input on the OneBox. When they measure the signal arriving at the OneBox, the pulses range from 0 to 5 V, but when the OneBox is powered on, they range from 1.7 to 5 V. They are using DO1 and GND (the one next to DO1) of the terminal digital output, where two wires go to the SMA1 rear input of the OneBox. They tried replacing the behavior board with an Arduino sending TTL pulses, and it worked fine. They ask: could it be that the Harp behavior board cannot actively pull the voltage low enough for the OneBox to reliably detect a logical “0” because the circuit operates as a high-side switch with a passive pull-down? The engineer working with us on the setup suggested that the safest approach would be to use a proper translator circuit to ensure the TTL signals are reliably detected by the OneBox. Do you know if a solution for this already exists, or would you recommend a particular approach? |
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Replies: 1 comment
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Their assumption is correct. The input of the OneBox has a low impedance, that prevents the DO1-DO3 of the Harp Behavior to properly drive the signal to 0 V and therefore unable to detect the logic '0'. If any of the Harp Behavior PORT0-2 is available, I would suggest to try using a port breakout board and connect to one of those digital outputs. Other alternatives are: lower the value of the passive pull-down resistor on the Harp Behavior (start with about one-quarter of the current resistor) or use a digital buffer (we typically build our own, not sure if there is anything out of the shelf already assembled). |
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Their assumption is correct. The input of the OneBox has a low impedance, that prevents the DO1-DO3 of the Harp Behavior to properly drive the signal to 0 V and therefore unable to detect the logic '0'.
If any of the Harp Behavior PORT0-2 is available, I would suggest to try using a port breakout board and connect to one of those digital outputs.
Other alternatives are: lower the value of the passive pull-down resistor on the Harp Behavior (start with about one-quarter of the current resistor) or use a digital buffer (we typically build our own, not sure if there is anything out of the shelf already assembled).