I'm road testing the Keithley Bench Digital Multimeter DMM6500. In this post, I investigate how to use the external trigger to start a measurement.
In this post, the setup is manual. In the next post I'll use LabVIEW to automate the process. |
Goal: I want to measure the voltage on a microcontroller GPIO pin just after it is set to high.
External Trigger
The DMM6500 has an external trigger input at the rear of the instrument.
It's a BNC connector that works on TTL levels.
Anything above 2 V is considered high. 0.8 V and lower is low.
The instrument can use this input to start activities. It can react on rising edge, falling edge or both.
The way to react on the trigger is via a trigger model. In this exercise, the model should wait for trigger, than measure.
I'm going to connect it to a GPIO output of a microcontroller. It's a MAXIM MAX32660, and I've configured it's GPIO to 3.3V, compatible with the TTL high input.
Further on in the post I'll show how to make the meter wait, and then take one measurement on that same GPIO when the trigger trips.
I'm using the LED output of the MAX32660 evaluation board, and want to measure the voltage on that pin when it's high.
Connections
I used a BNC to banana connector to connect the MAX32660 GPIO pin to the meter.
I'm also connecting the meter input to the LED pin of the MAX32660 evaluation board, that's P0_13, because I want to measure its voltage when put high.
(side note: this pin doesn't drive the LED directly. It drives a FET. But that's not relevant for this exercise)
Enable External Triggering
When you switch on the meter, it's in DC Volt mode. That's the mode I want to use, so we can leave it default.
To define the trigger model:
- navigate to Menu -> Trigger -> Configure.
- Press Insert After -> Wait -> Event 1 -> External In Trigger
- Press the * button next to Event 1 -> Rising
- Press Insert After -> Action -> Measure/Digitize
- Press Home
The trigger model is now configured. To enable it, press the Trigger key for 3 seconds.
- Press Initiate Trigger Model
The meter will now wait for the external trigger to fire on a rising edge. It will make a single measurement and stop.
Pressing the trigger button repeats the flow.
If you want to make multiple measurements, you can use a loop:
After the measuements (10 in this case) you can use the graph and stats functions to check measurements.
As promised, in the next blog I'll automate this in LabView.
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