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
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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
13,843
3,497
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
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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
5,053
784
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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1,168
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
4,813
1,331
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
4,813
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Only one resistor? Really? Wow, that's great! Which one?

ak

ErnieM likes this.
9. Colin55 Member

Aug 27, 2015
234
24
"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
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676
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
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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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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
3,421
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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
3,528
676
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.