Sword in the stone

Hello... I have created a system which can control "sword in the stone". Entertainment buisness.

I managed to make the 1. edition work 100%.


Then i thought, "now im gonna redo the board and make it work again". Just to be sure it wasent luck. It turns out, it WAS luck. . . I cant make my nr. 2 edition work. And it should be "almost" the same.


Problem discription:

I needa turn on relays with transistors. The board works, without load (relays), but when i add the relays i can see that the voltage from transistor to relay is dropping from 5v to 2v.

The circuit is seperated into 2 boards. The control board, and the H-brigde (relay) board. I tried using the H-brigde from the 1. edition (succesful) system, but it wouldent work.....

So im down to its not being the H-brigde board which are bad, but the control board. It seems it wont deliver the amp for the relays, which makes it drop in voltage.

SO. There "should" only be 1 difference between the 2 control boards. I used a high watt (a cheaper old kind) resistors to the non working control board, while i used "normal" reistors for the working control board. . . .

Im thinking... Can these old fashion high watt resistors, somehow draw some power from the circuit? Which then ends up in not having enough power for the relays?

Hope you can help..... Best regards Mikethk

View attachment 67095

Looking at your circuit, I think the problem is that you have the relay coils in the emitter of the transistors.
The problem is not due to using high power resistors rather than low power ones.

Try moving them to the collectors as I have shown in the attachment.

You may also want to reduce the value of R7 and R8 to 1 or 2 k rather than 10k.

JimB

Hi JimB. And thx for fast and advanced feedback.

I dont see why i should move it to collector instead emitter? What is the difference? I know it dossent work as a relay, but will there be a huge lost through the transistor?

Well you made my day, cause i figured out the problem... I checked if i had 10K on and yes i had ofc. . . BUT. I did not manage to break the cobberline underneath, so there was no resistor in use This was on the working board....
I removed the resistor on the non working board, and now it works....

Its nice cause for me its hard to understand that 10K could be a problem.... So you much be smart Atleast smarter than me...

Would you recommend me to use some 1k if they work, and why? Or should i just keep using non?

Best regards Mikethk

Mikethk said:

Hi JimB. And thx for fast and advanced feedback.

I dont see why i should move it to collector instead emitter? What is the difference? I know it dossent work as a relay, but will there be a huge lost through the transistor?

Click to expand...

Because with it in the collector the transistor acts as a switch, providing maximum voltage to the relay. In the emitter the transistor acts in an analogue manner, providing lower voltage to the relay, and wasting lot's of heat in the transistor.

You should always have it in the collector - it's extremely poor design to place it in the emitter.

I understand that..... I have no reason to put it there.... I believe i see it as a relay, but ofc. its not the exact same thing....

Could it be true that if the transistor werent very big, it could actually burn from the amp you try to pull through it, when placing relay at emitter?

But thx alot...

Mikethk said:

I understand that..... I have no reason to put it there.... I believe i see it as a relay, but ofc. its not the exact same thing....

Could it be true that if the transistor werent very big, it could actually burn from the amp you try to pull through it, when placing relay at emitter?

Click to expand...

Yes it could - there's no reason to ever do it that way, as it provides lot's of disadvantages and no advantages at all.

Mikethk said:

I understand that..... I have no reason to put it there.... I believe i see it as a relay, but ofc. its not the exact same thing....

Could it be true that if the transistor werent very big, it could actually burn from the amp you try to pull through it, when placing relay at emitter?

But thx alot...

Click to expand...

There's no problem with connecting a relay to the emitter of a transistor; just don't put the 10k resistor there (e.g. no resistor there at all).