Author Topic: Sebosfato Help Progress  (Read 16090 times)

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the probe arrived!
« Reply #64 on: November 12, 2015, 18:25:56 pm »
the probe just arrived i just re readed the manual and realized that it can measure 30kvp-p and it has only +- 10k insulation betweebn each input and ground... what this mean?

i think i will try to buy another multimeter and another probe 1000:1 40kv equal to the one i have so i can monitor both inputs an dont make this one burn...

The probe  costed me a total of 501 dollars plus 60% of taxes so something like 800$ in the end... i reveived less than 200$ or donation... and i also manneged to buy an oscilloscope =D i´m happy and ready to play...


i´m thinking of protecting the inputs of the probe with extra tvs to ground to avoid any overvoltage... i´m sure will mess around with wave form and al but will be sure to be protected... i was also planning some way that i could see if some abuse happen...

i will also protect my multimeters from now on to be sure i wont blow them...

for the multimeters i though of constructing a metal case for them and tie the tvs to inputs and ground and ground the case...
this will save the day when using the probe in the case the probe ground is left unconnected... ii guess this is why my 1000:1 40Mohm 40kv probe totaly carbonized my multimeter probably i forgot to connect ground once..


damn the programed obsolescence

really if you are willing to help i´m willing to help you too impeed your equipment to burn unecessarily

any ideas?
« Last Edit: November 13, 2015, 07:46:51 am by sebosfato »

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IMPROVEMENT ON MY FREQ GEN
« Reply #65 on: November 13, 2015, 09:56:30 am »
I have found a bug in my circuit using a different opamp than a comparator like lm 329 or a 741 amplifier... the bug is it will not oscillate because 555 timer capacitor is not being able to charge to the point it start to oscilate...

now i´m using the lm 318 and it has inside a couple of antiparallel diodes allowing only small voltage difference between inputs (small resistance) = bug

a normal opamp normally have high impedance at both inputs...

so if using a small resistance voltage pot divider to set into pin 2 a resistor can be add in series with it to increase its impedance... probably is a good idea to have a capacitor before this resistor to filter any pickup that can happen into the wiring of the potentiometer going to the ckt board...

the resistor can be high and capacitance still very low would filter more than enough

in this 318 the impedance will be limited by you... we need to add a resistor between the 6 pin of the 555 timer and the positive input of the 318 this way we ensure the capacitor reach the levels for triggering and threshold to set the oscillation...

for example my maximum timing resistance in the 555 timer is 115kohm and minimum 10kohm giving a coarse and fine tune pots and fix resistor.. this give me a ratio of change of 11.5 times... so this is the range the capacitors are to be chosen according to this range to provide a full range of frequencies...

for example i use 1 nf fixed than add 10nf with a swith than add 100nf with another switch to have the good range...

Now i have a question.... do  you think i shoud add the resistance all on the negative side of the 318 or divide it between the negative and positive side... anyone can help me decide which is better?

i have a 10kohm there

in simulation i found that 1Mohm in the path from voltage divider to pin 6 is enough to not affect the frequency if changing the voltage going into the negative pin of the 318 from 1/3 to 2/3 of the supply voltage...

the waveform coming out of the 318 is very sharp and it can create very good pulse width like 99%

i than pass this thru an inverter to get the signal from 0 to vcc more perfectly square... the output of the opamp normaly dont get down to zero..it goes from 1v to vcc or something like it...

any help to think this would be nice...


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how to make a voltage divider using math
« Reply #66 on: November 13, 2015, 11:24:55 am »
using a predefined pot for example you get 10kohm potentiometer and you want it to control the duty cycle from 0 to 100% you need it to vary from 1/3vcc to 2/3vcc... but for example if you wanted it to go from 25% to 95% how to know what resistors to use? simple... ohms law...

lets take the first example... if you get a 10kohm resistor is easy to see that if you add another two 10kohm resistors in either side it connecting to the vcc will already vary from 1/3 to 2/3 of vcc...

but why is that? well resistors in series share the same current... so basically what i´msaying is that finding the voltage variation you desire you simply calculate the current and from the current and anyother voltage you want you calculate for the resistors....

lets use an easy value for example if vcc is 5v 1/3 of 5v is 1,666v 1,666v/by 10kohm = 166microamps;;; (100% range)
if i wanted to vary from 25% to 95% ex than i need to recalculate the voltage variance i need

 now for example i want in my circuit that it goes from 2v up to 3,33 volts to go from 25% to 100% since i work with vcc 5v

to find the 25% i subtracted the min voltage for 0% duty from the voltage for half vcc where is 50% duty cycle... than divided the result by two and than sum with 1/3 vcc again... if vcc is 5v 25% will be than for 555 timer 2.008v

so i actually now wants to vary 1,33v instead of  1/3 of vcc so 133micro amps

hope it helps...

another thing is to calculate the frequency of the 555 use the formula f=0,7185/R*C you can calculate the factor if you measure the frequency to get the best aproximation for your chip or board.. sometimes it vary a little... factor=F*R*C

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Re: IMPROVEMENT ON MY FREQ GEN
« Reply #67 on: November 13, 2015, 15:19:47 pm »
I have found a bug in my circuit using a different opamp than a comparator like lm 329 or a 741 amplifier... the bug is it will not oscillate because 555 timer capacitor is not being able to charge to the point it start to oscilate...

now i´m using the lm 318 and it has inside a couple of antiparallel diodes allowing only small voltage difference between inputs (small resistance) = bug

a normal opamp normally have high impedance at both inputs...


so if using a small resistance voltage pot divider to set into pin 2 a resistor can be add in series with it to increase its impedance... probably is a good idea to have a capacitor before this resistor to filter any pickup that can happen into the wiring of the potentiometer going to the ckt board...

the resistor can be high and capacitance still very low would filter more than enough

in this 318 the impedance will be limited by you... we need to add a resistor between the 6 pin of the 555 timer and the positive input of the 318 this way we ensure the capacitor reach the levels for triggering and threshold to set the oscillation...

for example my maximum timing resistance in the 555 timer is 115kohm and minimum 10kohm giving a coarse and fine tune pots and fix resistor.. this give me a ratio of change of 11.5 times... so this is the range the capacitors are to be chosen according to this range to provide a full range of frequencies...

for example i use 1 nf fixed than add 10nf with a swith than add 100nf with another switch to have the good range...

Now i have a question.... do  you think i shoud add the resistance all on the negative side of the 318 or divide it between the negative and positive side... anyone can help me decide which is better?

i have a 10kohm there

in simulation i found that 1Mohm in the path from voltage divider to pin 6 is enough to not affect the frequency if changing the voltage going into the negative pin of the 318 from 1/3 to 2/3 of the supply voltage...

the waveform coming out of the 318 is very sharp and it can create very good pulse width like 99%

i than pass this thru an inverter to get the signal from 0 to vcc more perfectly square... the output of the opamp normaly dont get down to zero..it goes from 1v to vcc or something like it...

any help to think this would be nice...

Hey Seb, Im using
http://web.mit.edu/6.101/www/reference/lt1632.pdf
op amp in my circuit if it may help with you im fixing to order a few and can send you a cpl if you think they will help you.

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Re: Sebosfato Help Progress
« Reply #68 on: November 14, 2015, 01:49:04 am »
this seems a good one to use too! i will keep the lm318 as they work nice too and are pretty fast for now! Thanks a lot for the offer if you really can i would be happy to get to work with them and see if they work better somehow! but they don't seem to be very cheap opamp.. isn't?

i´m kind of seeing some pre triggering now i guess may be due to the 1 megohm resistor i added only between the pin 2 of the 555 timer and the positive input  of the lm318...

i added a 10kohm load and now the output is a flat square... it was ramping a little..

i will try feedback too to try get away with false trigering...

 i´m bit sleepy now.. i worked all day into this... there was a 318 burned and i was really not understanding it... so spent some time not really well..

also i did something wrong when copying from the protoboard to the pcb... i think the waveform is different than it should... i will try to use some jumper wires to fix... maybe i forgot to add a not gate somewhere..  but will fix...
 


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spike problem
« Reply #69 on: November 14, 2015, 17:36:43 pm »
Hello

My fracture cell circuit is working nice but it has some spikes during the off pulse just where the other pulse is turning on after the dead time...

I added many capacitors all around and didn't changed anything else than impede the spike to get into the outputs of the ics... but still the output waveform has its spikes
 

i found that is actually due to a small delay diference from the outputs of the inverter and the divide by two

i found in simulation that adding at least an inverter between the clock and input of the divid by two introduce a delay that almost take the spike away...

my question is...how to get rid of it?

at my analog oscilloscope it does not show up.. the spike has around 22ns

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answer
« Reply #70 on: November 16, 2015, 05:09:58 am »
the answer was to put a inverter between the input of the divide by two and the clock source... also i reduced the gain of the lm318 and the waveform impreved... using positive feedback..10Mohm

still not perfect but is already working and clean...

what is happening is at lower frequency it seems to not be able to maintain small delay between the pulses... don't really understood why yet

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Re: Sebosfato Help Progress
« Reply #71 on: November 18, 2015, 07:43:23 am »
now its all woking pretty much fine.. i´m just trying to solve some ghost oscillations that some times appear... but the wave forms are fantastically great... there is a coarse and fine tune pots 100k and 10k respectively... with 5kohm in serie...  this with 555 timer and 1nf capacitor generate from 5k to 70khz

there is some workaround i had to do on the opamp to make the wave form cleaner... specially at lower frequency it kind of generate some spurious signals.. its really very short pulses but should not be there anyway... i believe its picking up some noise from the flipflop since its very close in the pcb that might be the problem... maybe i change that...

so far i had to change some of the parameters to make it work... reduce the feedback resistance and the input resistance.. this makes it more stable but still not yet satisfactory...