# Low Level Pulse Signal over 500ms

Discussion in 'The Projects Forum' started by Dan Burfield, Feb 19, 2016.

1. ### Dan Burfield Thread Starter Member

Aug 12, 2010
10
0
I am trying to get a small 5v video camera to work. Eachine 2202M.
It requires a "Low level pulse signal to trigger start/stop video recording. Pulse needs to be over 500ms. Needs to be less that 3.3v."

How do I generate this pulse using 5v on/off momentary switch?

Dan

2. ### crutschow Expert

Mar 14, 2008
13,477
3,362
Don't understand what you mean by "Needs to be less that 3.3v."
So it can't be 5V?
How much less?

3. ### Colin55 Member

Aug 27, 2015
204
21
You can deliver 5v via a resistor.

4. ### Dan Burfield Thread Starter Member

Aug 12, 2010
10
0

This is from the instructions online:

3PINS Control signal

1. Low level pulse signal triggering to start/stop photo with one I/O interface, pulse need to be between 100ms ~ 490ms, otherwise it is invalid.

2. Low level pulse signal triggering to start/stop video with one I/O interface, pulse need to be over 500ms, otherwise it is invalid.

The peak voltage of input control signal needs to be less than 3.3V.

5. ### ScottWang Moderator

Aug 23, 2012
4,925
777
Using a ne555 monostable circuit to set up the trigger time to 0.5S or more.
If the output voltage is too high then you can using a voltage divider to reducing the voltage.
555 Monostable Circuit Calculator online.

6. ### Alec_t AAC Fanatic!

Sep 17, 2013
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1,135
Can you post a link to those online instructions, so that we can see them in context? It's odd that a 5V camera would require an input control signal to have a 3.3V maximum.

7. ### AnalogKid Distinguished Member

Aug 1, 2013
4,685
1,297
Not really. 5 V power because that's everywhere on USB ports and chargers. 3.3V controls because the chips are running on 3.3V after an onboard refgulator.

ak

8. ### AnalogKid Distinguished Member

Aug 1, 2013
4,685
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Only one resistor? Really? Wow, that's great! Which one?

ak

ErnieM likes this.
9. ### Colin55 Member

Aug 27, 2015
204
21
"You can deliver 5v via a resistor.
Only one resistor? Really? Wow, that's great! Which one?"

One resistor can be used, It depends on the input impedance of the device you are controlling.

10. ### dl324 Distinguished Member

Mar 30, 2015
3,376
651
Can you post a PDF of the instructions? I saw somewhere that the requirements for video and photo were reversed. If that's the case, the longer than 500mS pulse would take a picture, not record video.

Are you using this in a drone, or are you repurposing?

Aug 12, 2010
10
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12. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Is that switch mechanical (push-button) or electronic (e.g. from a MCU)?

13. ### Dan Burfield Thread Starter Member

Aug 12, 2010
10
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Hey Alec- it would be mechanical.

14. ### dl324 Distinguished Member

Mar 30, 2015
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651
Check your camera to see if the manual is correct. If you actually need a negative pulse of 100-490mS to start video recording, the circuit below will do it:

IC1 is a single TinyLogic Schmitt Inverter.

The time of the low pulse is $\small -t = RC ln\frac{1.0V}{3.3V}$
200K and 1uF will give about 240mS. Pulse width depends on the negative threshold voltage, which I assumed to be 1.0V (typical at VCC=3.0V).

If you really need a 500mS+ pulse to start video recording, just hold the switch closed for a second.

The pulse will be generated when power is applied. I assume taking a picture would stop video recording, so you can press the switch for a second to stop recording. Then press the switch again when you want recording to start.

15. ### ronv AAC Fanatic!

Nov 12, 2008
3,393
1,451
I think I see your concern. If you want it to work from the 4.2 volt battery you can drop the voltage to 3.3 with a restive divider.

16. ### Dan Burfield Thread Starter Member

Aug 12, 2010
10
0
Gentlemen, thank you for sharing your knowledge. I am slowly poking my way through DL324's design. I am using it as a map, finding the parts/data sheets, for the Schmitt inverter specifically and drawing pic of how i will solder it all together.

I have one concern at the moment. The inverter I found seems awfully small for soldering. Is there something bigger/more friendly that I am missing?

Thanks again so much for the help, I'll keep you updated with my progress.

-Dan

17. ### dl324 Distinguished Member

Mar 30, 2015
3,376
651
My intent was to save you weight and area by specifying a surface mount component. If that isn't a concern, there are many ways to get the pulse you want. You could switch to through hole components (e.g. 74C14) but you'll have 5 unused inverters and should probably consider other solutions.

I recommend that you test any circuits before doing final assembly and confirm whether you need a 100-490mS or 500+mS pulse.

The schematic I gave will give something in the 125-410mS pulse for the min/max threshold voltages for the inverter and a 20% tolerance (total) on the R and C.