Need to know how to create a pulsed ground in a 12v system

Thread Starter

bobiowa

Joined Jan 25, 2022
24
Hi all,

i have been trying to integrate a sound module in a vehicle. Basically what it does is play a mp3 file when its channel that the sound sits on (there are 6 channels/sounds) receives a ground. Unfortunately what the manufacturer (in China of course) didnt tell me was that of all the options to control each channel the one that allows a solid ground (ie - flipping a switch to ground and sending to the module) locks up the module and wont allow other channel sounds to play unless the switch's ground is removed. So in essence what i am seeing is that i need to be able to convert any of the channels that i am using switched type ground to "pulsed" grounds - I just need a short pulse like pushing a momentary button to do it.

Is there any way to convert a solid ground to a one pulse ground easily?

Although I can connect wires in a car, I'm pretty electronics ignorant so if you would please be aware of this when responding :)

Thanks for any insight you guys can share
 

Irving

Joined Jan 30, 2016
3,845
What is going to drive the 'pulsed ground', and does it need to be grounded while the clip is playing?

A simple MOSFET will pulse the ground selection.,,
 

Thread Starter

bobiowa

Joined Jan 25, 2022
24
a switch going to ground is what i think you meant driving the pulsed ground, and no once the pulsed ground is sent thats all it needs. For example, one scenario is that i have a reed switch that goes to ground when the license plate is in the up position (the license plate is moved underneath the car when parked) so i have a magnet on the lever actuator that triggers the reed switch to go to ground - my problem is that is stays grounded the whole time and the wire from the reed switch goes to the module that is expecting it to be just momentary (one little blip of a ground) is what i need (even though the reed switch will stay grounded). I hope i am explaining this right
 

Irving

Joined Jan 30, 2016
3,845
How many 'input' channels do you need? There isn't an 'off-the-shelf' solution to this; its not hard to resolve but needs some electronics. Whereabouts are you?
 

djsfantasi

Joined Apr 11, 2010
9,156
It sounds as if simply grounding the trigger locks up the unit.

Perhaps a 555 one shot and an N-channel MOSFET might work.The 555 trigger pin would require a pullup resistor and a toggle switch to ground. Should be powered from the accessory power.
 

Thread Starter

bobiowa

Joined Jan 25, 2022
24
It sounds as if simply grounding the trigger locks up the unit.

Perhaps a 555 one shot and an N-channel MOSFET might work.The 555 trigger pin would require a pullup resistor and a toggle switch to ground. Should be powered from the accessory power.

Here is a link to the module that explains its behaviour ( https://www.electronics123.net/amazon/datasheet/FN-AL6T Multifunctional MP3 Player.pdf )
- and "yes" it locks up the unit when input is static ground. However on mode 1 which allows a channel to loop the sound over and over it works but also wont allow any other sounds to play on other channels until that ground is removed.
 

Irving

Joined Jan 30, 2016
3,845
Can't see the link to the module... there's a few on AliExpress...

It sounds as if simply grounding the trigger locks up the unit.

Perhaps a 555 one shot and an N-channel MOSFET might work.The 555 trigger pin would require a pullup resistor and a toggle switch to ground. Should be powered from the accessory power.
In principle yes, but gets messy for 3 or more channels - I'm thinking a 1-chip solution...
 

Thread Starter

bobiowa

Joined Jan 25, 2022
24
Thanks for the responses, Im not sure what the schematics are telling me but i see 12v in a couple of them, this sound player only accepts a ground on the inputs - is the 12v used somehow to do a reset or something? The idea of a capacitor inline on the wire going to the ground is interesting in the i at least know how i could wire that. Would it work?
 

crutschow

Joined Mar 14, 2008
34,286
Im not sure what the schematics are telling me but i see 12v in a couple of them
In my circuit, that 12V just represents the battery voltage going to the Jingle Player with the Rsim resistor simulating whatever is in the player to the control output.
There is no direct connection from the 12V to my circuit other than through the control switch contacts of S1.
The idea of a capacitor inline on the wire going to the ground is interesting in the i at least know how i could wire that. Would it work?
The capacitor is in a common configuration that generates a short pulse, which should work for your requirements.
 

LowQCab

Joined Nov 6, 2012
4,029
A Capacitor has to have any Charge left over in it, Dis-Charged, before it will create another Pulse.

The Circuit I provided requires a Switch connected to 12-Volts,
in order to create a 0.25-Second Pulse to Ground.
It will easily fit on a 2" X 2" square Perf-Board, and is a great beginner project.
It's hard to get it wrong.

Have You ever read a Spec-Sheet for an Electronic Part ?

I provided a DigiKey Part-Number for the TL431-Precision-Voltage-Reference.
The other parts are all generic.
.
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