pulse train generator

[unlv007]

I want to make a simple square pulse generator producing a +5V pulse for 5ms followed by off period=20ms. How do i synthesize it using readily available ICs, transistors etc? Any ideas?
Thank you very much.
Regards

 

[mneary]

Is 5% accuracy good enough? When you say 5V, do you really mean a logic "1" for 5V logic?

Sounds like a job for a 555.

 

[KMoffett]

**broken link removed**

The second or forth circuit.

Calculators are available on that site to select components for your on and off times.

Ken

 

[unlv007]

How do you compare 7490 and 555? I guess 555 is a classic circuit, ,but how is its performance? please let me know.

yes 5% should be good enough, the pulse train should be 5V=on and 0V=off .
So logic 1=5V.
thank you very much.

 

[unlv007]

Thanks once again for your help

 

[KMoffett]

I don't think the 7490 will give you the time periods you are looking for. Maybe a CMOS 4060 internal oscillator set to 200Hz and with a reset after the 5th count?
https://www.fairchildsemi.com/ds/CD/CD4060BC.pdf

Ken

 

[unlv007]

Is it possible to build a pulse generator with controllable amplitude? The amplitude may vary from 0 to 5V? Can LM555 implement this?

 

[KMoffett]

Yes...a potentiometer as a variable voltage divider, from pin 3 of the 555 to ground...voltage from wiper to ground can be varied from 0 to 5v. Simple, but with cannot drive any significant load.

Ken

 

[unlv007]

If i want to increase with voltage of the pulse to 40V and be in the same timescale,that is pulse time period in ms, how should i go about it? Should i build an amplifier or should i use a new IC?
Thanks.

 

[KMoffett]

unlv007,

I think at this point you need to describe > in detail < exactly what you are trying to do. What are you going to drive with this pulse generator. It helps eliminating a lot of wasted effort...on our part..as well as yours. Or is this just a mind experiment?

Ken

 

[unlv007]

the voltage pulses will be used to trigger a chemical reaction. The chemical reaction usually has been done using a constant DC voltage or current source but we are trying to use pulses and see if there is any change in behavior. We usually apply 40V DC or 50mA steady state DC. We have an amplifier that claims to amplify pulses. My final aim is to obtain pulses of 40V or 50mA peak value. It is easy to build 5V pulses using LM555 but i suspect it will be difficult to amplify the pulses if the frequency is high. The solid state device based transistor amplifiers may not have such high switching speeds. So, how do i get a 40V or 50mA pulse?

 

[blueroomelectronics]

What chemicals? Are you making Hydrogen?

 

[unlv007]

its an oxidation reaction. My aim is 40V pulse or 50mA pulse. The amplifier i have is pretty expensive. My first preference is to get pulses without amplifier. If that does not work, i will use amplifier. Can any IC produce 40V or 50mA current pulses directly?

 

[jbeng]

What's the DC resistance of the reaction cell?
Jeff

 

[unlv007]

the resistance is non linear. It changes as reaction proceeds. We prefer to use a DC current to drive the reaction.Typically with 30mA constant current, the voltage drop across the reaction cell rises to 35V in 3-4 secs, remains constant later on. As I=const, and V=IR, resistance increase due to oxide growth in the reaction cell is monitored by measuring voltage.
I want to build a pulse drive circuit that can drive the above load. So, the task is
build a current pulse generator that can produce pulses of say 30-50mA , the compliance voltage of the current source must be atleast 35V, but 60V will give good margin. How do i go about it?