7404 max output current is 16mA
You'd be better off without it.

 

LM358 will also struggle with anything above 10mA.

 

ok, then how to increase the current a little bit?

 

I have several 50mA meters. They are a resistor inside. I remove the shunt resistor, and the meters are now 100uA meters.

 

I have several 50mA meters. They are a resistor inside. I remove the shunt resistor, and the meters are now 100uA meters.

I repaired mine and I know it's inside very well by now. It has no internal resistor like yours have. I had to add that 200R for the needle to stay in the middle of the dial, but thats it.
- another minor tweak:

before it had a 1k in series with that pot. Removing it, is a tiny bit better and also simplify the cct.

 

back to the box then - eh, pitty we couldnt find a nice project for it.
not all wars can be win, right?

 

update:

note: I made 3 movies before that were short, so I decided to make a single movie with all 3 in 1. I also added a 4th movie in continuation.
I made it simple to skip everything you may have seen already with a very easy link list in the movie description there on YT.
Click on those links and you will be teleported to the right part/movie.
Thank you.

 

With a little modification, You can use this as a weight scale, sensitive in the microgram range.
The unknown weight can be put on the end of the needle. Gravity changes the position of the needle, and You can compensate against it by driving a current through the coil. The original position can be sensed somehow. Then, the current is proportional to the unknown weight - can be digitized, sent through the Internet or something.

 

Hey, what do you think of all this goodness:
"it's the how I made it" movie