Shorting stuff out on purpose, a whole new ball game?

Thread Starter

ulms

Joined Mar 19, 2024
55
Hello, I'm 62, I'm new to this. I was the guy you came to to fix your car back in the 70s. I just retired, a construction worker, I said I'll be damned, I'm going to learn what the hell these little things do in the cars keep people keep bringing me to fix. I'm studying BJT transistors. I'm making all kinds of circuits, I'm copying circuits from schematics on line I'm adding two or three of them together to make what I want to make. But most importantly I want to say this about electronics as I see it. Shorting something out which was considered a huge No-No in my day is business as usual in these circuits at these voltage and current levels. Is that correct?
 

BobTPH

Joined Jun 5, 2013
9,274
Hello, I'm 62, I'm new to this. I was the guy you came to to fix your car back in the 70s. I just retired, a construction worker, I said I'll be damned, I'm going to learn what the hell these little things do in the cars keep people keep bringing me to fix. I'm studying BJT transistors. I'm making all kinds of circuits, I'm copying circuits from schematics on line I'm adding two or three of them together to make what I want to make. But most importantly I want to say this about electronics as I see it. Shorting something out which was considered a huge No-No in my day is business as usual in these circuits at these voltage and current levels. Is that correct?
No. Give us an example.
 

WBahn

Joined Mar 31, 2012
30,298
Hello, I'm 62, I'm new to this. I was the guy you came to to fix your car back in the 70s. I just retired, a construction worker, I said I'll be damned, I'm going to learn what the hell these little things do in the cars keep people keep bringing me to fix. I'm studying BJT transistors. I'm making all kinds of circuits, I'm copying circuits from schematics on line I'm adding two or three of them together to make what I want to make. But most importantly I want to say this about electronics as I see it. Shorting something out which was considered a huge No-No in my day is business as usual in these circuits at these voltage and current levels. Is that correct?
We really need to see some specific examples of what you are referring to.
 

Thread Starter

ulms

Joined Mar 19, 2024
55
We really need to see some specific examples of what you are referring to.
I recently retired and now that I have all the time in the world I can't seem to remember to water my seedlings for this Summer's vegetable garden. I built a moisture sensor, I bought a hall effect door sensor that sends me a Wi-Fi message and I was getting notified when the soil was dry. Everything was fine until I noticed the plant with the electrodes in it was diminutive next to all the others. Closer observation revealed that the electrodes 18/8 stainless steel were eroding. Electrolysis I'm sure. So I decided I would want to turn this circuit on and off for 20 seconds per hour. I built this 555 timer circuit. Take special note of what I labeled green wire coming from transistor Q3 being the key and success to this. Something in my gut said to do it but I don't fully understand what I did.IMG20240418122650.jpg
 

MrChips

Joined Oct 2, 2009
31,086
I recently retired and now that I have all the time in the world I can't seem to remember to water my seedlings for this Summer's vegetable garden. I built a moisture sensor, I bought a hall effect door sensor that sends me a Wi-Fi message and I was getting notified when the soil was dry. Everything was fine until I noticed the plant with the electrodes in it was diminutive next to all the others. Closer observation revealed that the electrodes 18/8 stainless steel were eroding. Electrolysis I'm sure. So I decided I would want to turn this circuit on and off for 20 seconds per hour. I built this 555 timer circuit. Take special note of what I labeled green wire coming from transistor Q3 being the key and success to this. Something in my gut said to do it but I don't fully understand what I did.
Circuit rotated and enhanced:

20240418 AAC member.jpg
 

MrChips

Joined Oct 2, 2009
31,086
Hello, I'm 62, I'm new to this. I was the guy you came to to fix your car back in the 70s. I just retired, a construction worker, I said I'll be damned, I'm going to learn what the hell these little things do in the cars keep people keep bringing me to fix. I'm studying BJT transistors. I'm making all kinds of circuits, I'm copying circuits from schematics on line I'm adding two or three of them together to make what I want to make. But most importantly I want to say this about electronics as I see it. Shorting something out which was considered a huge No-No in my day is business as usual in these circuits at these voltage and current levels. Is that correct?
You've heard the old story, the repair bill to fix the motor came to $1005.00
"Why the $5, and the $1000?", asked the client.
"$5 is for hitting the motor with this hammer", came the reply.
"$1000 is for knowing where to hit!"

It all comes down to know-how. When you know what you're doing, nothing is impossible.
 

Thread Starter

ulms

Joined Mar 19, 2024
55
Did you design this circuit?
Well in this manner Bob. The first thing I did was made a simple moisture sensor. Then I googled how to make an inverter with a transistor because I wanted the opposite signal. So I put that in front of the moisture sensor. Then I needed a timer with tall demands 10 seconds on 1 hour off so I put that in front of everything. It's sort of mine made up of the work of others.
 

BobTPH

Joined Jun 5, 2013
9,274
What you have done is used a low side switch to switch ground on the right side of the circuit.

That is not commonly done, mainly because there could easily be other paths to ground in a connected circuit.

Instead, use the output of the ‘555 to provide the 5V to the regulator, and connect the two grounds together. Or, better yet, use a P-channel MOSFET to switch power to the circuit. Or even better, use a regulator with an enable input.

When combining circuits, connecting their grounds is the first step, unless there is a reason not to.
 

WBahn

Joined Mar 31, 2012
30,298
It looks like you are using the 555 timer to make/break the ground to your 3.3 V regulator. You can play games like that and make things work, but there are demons that hide in those swamps.
 

Thread Starter

ulms

Joined Mar 19, 2024
55
It looks like you are using the 555 timer to make/break the ground to your 3.3 V regulator. You can play games like that and make things work, but there are demons that hide in those swamps.
Bob, Wbahn and MrChips, It didn't really gel with me but it was the only thing that worked. Thank you very much both of you. Any ideas on how to get rid of RC1 and replace it with a transistor I can't seem to make that happen.
 

Thread Starter

ulms

Joined Mar 19, 2024
55
What you have done is used a low side switch to switch ground on the right side of the circuit.

That is not commonly done, mainly because there could easily be other paths to ground in a connected circuit.

Instead, use the output of the ‘555 to provide the 5V to the regulator, and connect the two grounds together. Or, better yet, use a P-channel MOSFET to switch power to the circuit. Or even better, use a regulator with an enable input.

When combining circuits, connecting their grounds is the first step, unless there is a reason not to.
Bob that actually works but the 555 chip gets really hot I can smell it. So all the power is running through it yes? So I'll do something with another transistor there to handle the load. Thanks again.
 
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