# detecting PWM without an oscilloscope

#### john2k

Joined Nov 14, 2019
146
I have a power source on my car that by default is PWM and i've found a way in the ECU configuration to disable PWM but I want to know if the setting has worked. I don't want to have to buy an oscilloscope just to test this. Is there a cheap way to just check if its pulsing or not?

#### BobTPH

Joined Jun 5, 2013
3,319
Measure the output on a multimeter on the AC voltage range. If PWM is disabled, it should read near zero.

Bob

#### schmitt trigger

Joined Jul 12, 2010
440
Some multimeters who have a frequency function, can be used to detect whether the PWM waveform has been disabled or not.

#### AlbertHall

Joined Jun 4, 2014
11,317
Measure the output on a multimeter on the AC voltage range. If PWM is disabled, it should read near zero.

Bob
That only applies if either of these are true.
1. The PWM output voltage is zero when disabled.
2. The meter AC ranges are capacitor coupled. Many cheap meters will show a reading on AC ranges with DC input.

#### drc_567

Joined Dec 29, 2008
1,112

There are several low cost oscilloscope kits on the market. Reviews seem to be favorable.

#### dl324

Joined Mar 30, 2015
12,871
There are several low cost oscilloscope kits on the market. Reviews seem to be favorable.
After seeing that scope mentioned several times, I bought a fully assembled one with a case (that needed assembling) for less than $20. For the price, you can't complain. There's a hack on GitHub to add a second trace, but it costs you some bandwidth. For less than$40, you can have a battery operated 5MHz FNIRSI PRO DSO.

#### Delta Prime

Joined Nov 15, 2019
1,024

#### BobTPH

Joined Jun 5, 2013
3,319
That only applies if either of these are true.
1. The PWM output voltage is zero when disabled.
Only if disconnected from the load.
2. The meter AC ranges are capacitor coupled. Many cheap meters will show a reading on AC ranges with DC input.
Easily tested and easily remedied.

Bob

#### SamR

Joined Mar 19, 2019
3,411
These are pretty handy to have about. Pocket sized (about US cigarette pack size) and USB rechargeable. ~\$25 US
DSO FNIRSI 150 Digital Oscilloscope full assembled with P6020 BNC standard probe|Oscilloscopes| - AliExpress

Specifications:
• Maximum real-time sampling rate: 1 MSa/s
• Analog bandwidth: 0 - 200 KHz
• Sensitivity range: 5 – 20 mV/div
• Maximum input voltage: 50 Vpk (1X probe)
• Input impedance: 1M ohms/20pF
• Accuracy: 12 bits
• Record length: 1024 points
• Coupling modes: DC / AC / GND
• Time Base Range: 500s/Div – 10us / Div
• Trigger modes: Auto, normal, and single
• Trigger position: Center of buffer
• Supply voltage: DC 9 V (8 – 10 V)
• Current consumption: ~120 mA @ 9 V
• Main board size: 94 x 65 mm (3.7 x 2.56 in)
• Analog board size: 65 x 47 mm (2.56 x 1.85 in)
• Screen size: 52 x 40 mm (2 x 1.57 in)
• Package size: 14.5 x 10 x 3.7 cm (5.7 x 3.94 x 1.45 in)
• Package weight: 179 grams (6.33 oz)
Key features:
• Adopts ARM Cortex-M3 processor (STM32F103C8), and includes a 2.4-inch color TFT display screen
• Used for secondary development on the basis of this kit, for example, it can be changed to millivoltmeter, data loggers
• Come with instructions, easy to install and operate
• Auto/normal/single trigger modes, easy to capture the moment waveform
• Available rising or falling edge trigger
• Observable previous waveform before trigger (negative delay)
• Can freeze waveform display at any time (HOLD function)
• Waveform parameter digital display, including frequency, period, pulse width, duty ratio, MAX./MIN./AVG./Peak-Peak/virtual values
• Waveform storage function: Will not lose the waveform after powering off
• Short-circuit and open-circuit detection: Can help the user find out the soldering error
• TFT controller recognition function
• The SMD has been soldered, more suitable for electronic beginners