# Digital Timer for Video

#### DC_Kid

Joined Feb 25, 2008
806
I am looking for a "small" large LED/LCD digital timer that can display 5digit in milli-sec, or xx.xxx (sec.msec).
Just a cheap non certified DC powered timer. Something like this one. One inch tall numbers would be great.

I am filming some stuff using two goPro cameras on different angles and want a timer in the video so I can sync them later in editing.

Any recommendations?

Joined Mar 10, 2018
4,057
Is the frame rate of the camera < 1 milli second ?

I am thinking at 120 frames/sec your timer only needs to resolve ~ 100 mSec.

Regards, Dana.

#### DC_Kid

Joined Feb 25, 2008
806
120x/sec = one x event every 8.33msec
1s/120 = 8.33msec

But for what I am filming the FPS dont matter, I need the actual time in the video, and I need to see the msec #, etc.

#### Sensacell

Joined Jun 19, 2012
2,894
Most multi-digit LED displays are multiplexed, at high frame rates, some digits might start to flicker or disappear altogether.

#### MrChips

Joined Oct 2, 2009
24,241
Most multi-digit LED displays are multiplexed, at high frame rates, some digits might start to flicker or disappear altogether.
Good thinking. The TS should build his own timer using non-multiplexed displays. That is not difficult to do with a straight 5-digit BCD counter design.

#### AnalogKid

Joined Aug 1, 2013
9,362
The max timing range of what you describe is just over 1-1/2 minutes. That's not much unless you are shooting very short segments.

And, as above, unless you have all of your camera frame rates synchronized, you will not see the same number in each frame captured at the same "instant".

And and, are you sure there isn't a time code embedded in the video data format? NTSC video started embedding time codes in the 1970's.

ak

#### DC_Kid

Joined Feb 25, 2008
806
1.5min counter is long enough for my needs as I am filming events one at a time that only take a few sec to complete.

Having frame shutter sync'd is not a big issue as I can slide each video in editor to get things to align. As example, if I do PIP in editor the videos should look sync'd even though the frames of each camera do not align 100%, etc.

My editor does have a TC box but that doesn't help too much because it only shows time from start, does not appear to be real video TC.

Also, having the timer in the video is not so I can sync multi video streams, it's to have a relative clock in the video so I can see time vs event in the video.

I can build my own, but wanted a simple COTS.
I could simply set 1st clk to 1kHz and then chain them
https://www.electronics-tutorials.ws/counter/bcd-counter-circuit.html

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#### AnalogKid

Joined Aug 1, 2013
9,362
Three of these in series will do what you want without any multiplexing flicker, but the digits won't be evenly spaced. You could get larger displays, mount them in a frame of some kind, and run wires down to the boards.

https://www.ebay.com/itm/Digital-2-...=item259373b28e:g:b1oAAOSwDk5T4fn-:rk:91:pf:0

Here is one based on a popular 3-digit counter.
https://www.ebay.com/itm/3-Digit-LE...K7LA:sc:USPSFirstClass!43220!US!-1:rk:32:pf:0

Not sure if this will do what you want.
https://www.ebay.com/itm/RF-6-Digit...=item1ef1609526:g:xUYAAOSwgcdcIeCb:rk:17:pf:0

ak

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#### DC_Kid

Joined Feb 25, 2008
806

#### MrChips

Joined Oct 2, 2009
24,241
Hi AnalogKid
Those wont work, but this one came close
https://www.ebay.com/itm/4-Digit-Up-Down-Counter-Kit-Requires-Assembly/162423359594

But unfortunately they use a ~15msec debounce on each rise & fall (done in software) which makes it no better than a 1/35s counter.
http://www.alltronics.com/mas_assets/acrobat/KIT_129.pdf

I did order the item from amzon that I had posted, will see if that thing can count msec on timer-2 and sec on timer-1. If it doesnt then i'll just make my own.
That is a multiplexed display. You don't want that.

#### DC_Kid

Joined Feb 25, 2008
806
That is a multiplexed display. You don't want that.
Which one is a mplex ??

#### MrChips

Joined Oct 2, 2009
24,241
Which one is a mplex ??
Both of them linked to in post #9 are multiplexed displays.

If you see transistors in the circuitry, it is most likely for multiplexing.

#### DC_Kid

Joined Feb 25, 2008
806
Both of them linked to in post #9 are multiplexed displays.

If you see transistors in the circuitry, it is most likely for multiplexing.
It's the same unit, not two different ones.
Although I did order the amzon item I did also order some discrete parts to build my own using five 1" tall 7 segment LED's.

#### DC_Kid

Joined Feb 25, 2008
806
I canceled the amzon item, I am just making my own. Had to order ~$40 worth of parts from Mouser, using Kingbright 1" tall 7segment LED displays. I already made the needed voltage supply (LDO's) and 1kHz signal (non precision using 555). For my needs this will work. I was just hoping for a low cost COTS but failed to find it. When you cant find it then just make it #### MrChips Joined Oct 2, 2009 24,241 I canceled the amzon item, I am just making my own. Had to order ~$40 worth of parts from Mouser, using Kingbright 1" tall 7segment LED displays. I already made the needed voltage supply (LDO's) and 1kHz signal (non precision using 555). For my needs this will work. I was just hoping for a low cost COTS but failed to find it. When you cant find it then just make it
Sometimes that's the only way to go. If you need help with the design post us your schematics.

#### DC_Kid

Joined Feb 25, 2008
806
Sometimes that's the only way to go. If you need help with the design post us your schematics.
Ah, ez pz. I am using 9v batt to 7805 which powers everything, minimal components. NE555 to get 1kHz (used one pot so it can be "precisely" tuned to 1kHz). I am just doing this BCD/driver → https://www.electronics-tutorials.ws/counter/bcd-counter-circuit.html

I am not even using resistors to each LED, I just used two 1N4001's in series to knock down the voltage to 3.5v and that feeds all the LED segments (the Kingbrights are 4v @ 20mA per segment). 35 resistors vs two diodes . I'll toss in a momentary to reset the counters, etc. The whole thing is just to have a visual marker in the video, and its less about actual time. I suspect I could have done something like a spinning disc that has some marks on it (like one of those handheld batt powered mini cooling fans that blow no air on you, but mark one fan tip with a line/arrow using sharpie) because that would give enough visual to sync video in editing. But I wanted something more "cool"

When it's done I shall post a pic.

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#### MrChips

Joined Oct 2, 2009
24,241
74LS00 series is power hungry compared to CMOS.
You could be have been using CD4029 BCD counter and CD4511 decoder driver. Then you don't need a 7805 regulator.
You still need current limiting resistors on the LEDs.
There are other BCD counters to choose from.

#### DC_Kid

Joined Feb 25, 2008
806
74LS00 series is power hungry compared to CMOS.
You could be have been using CD4029 BCD counter and CD4511 decoder driver. Then you don't need a 7805 regulator.
You still need current limiting resistors on the LEDs.
There are other BCD counters to choose from.
I spent no time choosing the "best" parts. It wont be used often so batt life is of no concern.
Why the need for resistors? The led's are 4v20mA.

#### DC_Kid

Joined Feb 25, 2008
806
5v supply running through two 4001's w/o resistors. All 7 segments run at just ~60mA (I don't know how these low cost MIC power supplies round the amp meter, so it could be 69mA for all I know). So with my 5 digit timer the display itself will run max mA when all are "8", so just ~300mA peak, plus a little to run the IC's and some loss in LDO's. Should be fun

#### AnalogKid

Joined Aug 1, 2013
9,362
I don't see any ICs in the photo. But if you are relying on the internal impedance of the 4001 gate to limit the LED current, the gate will not last long. You really do need current limiting resistors (1 per segment) to prevent driver and display damage.

An LED is like a signal or rectifier diode in that it has no mechanism for limiting the power it dissipates. An LED rating of 4 V and 20 mA means that if you externaly limit the current through the LED to 20 mA, the voltage drop across it will be 4 V. If you apply a 4 V source with lotsa current available, the LED will try to pass all of it and fail.

With a 5 V source, you need to drop 1 V at 20 mA across the current limiting resistor. With Ohm's Law, this works out to 50 ohms. 47 or ohms are the closest standard values at 5% tolerance.

ak