FJN3303 Substitute ? KSP44 ?

[narg]

Hi,

I'm mounting a Geiger counter based in your's, but i'm dealing with the problem that I cant find fjn3303 in Portugal
I'm thinking about ksp44 and i have it on hands but i don't know why it's not working as expected (yes i'v seend that pinout is diferent)
With 10ohm on vr1 i get 230v readed with multimeter if i reduce the value of vr1, it goes to zero volts. Shall I change vr1 for a 100ohm trimmer and remove R8 with a jumper ?


Should 555 timer be cmos or a ne555 is enough ?

I cant see polarity on my sbm-20 tube (it marks cbm-20) i think is the same thing, one side have the brown "plastic" the other is all metal what should be the - or the + of tube, i suppose that the based on this picture http://sbm-20.com/images/sbm-20u.jpg the positive pole should be the one without the brown "plastic"
Am I correct ?

[mightyohm]

Yes, that is the correct polarity.

What is the input impedance of your voltage meter, and are you adding any series resistance?

[narg]

From what I'v readed my input inpendance of DMM is 10 M ohm

Now i'm getting geiger counting, i have had a problem with a ground soldering of 555.


With KSP44 i'm getting on DMM 220v and i'm getting betwen 16 to 50 CPM's in background having more incidence on 30 CPM's

I have changed the VR1 from a 100 Ohm (easier to get and removed R8 from circuit (current value 25 Ohm = 10 from your circuit VR and 15 From R8)

Do you have any schematic how to put it comunicating with arduino witout changing the voltage of geiger, a ttl shifter ! to put an LCD

[mightyohm]

I don't have a schematic, but you should be able to make one from the description here:
http://mightyohm.com/blog/2012/05/pics- ... ker-faire/