Newbie Help Needed

Hi all,

Firstly let my apologize for being a complete newbie and knowing NOTHING about electronics.

You help (and patience) are appreciated.

I want to produce is a device that delivers a 9 volt dc charge to two electrodes at a current of between 0.25 - 3 milliamps.

A dial should control the current at steps of 0.25 milliamps.

A timer is also required between 1 - 60 minutes.

Finally, I've seen on some dc devices (such as tens machines) quote a frequency. Now I understand that an AC device has a frequency as the direction of the current alternates. But what does this frequency refer to if it's a dc device? Or is it's output current alternating if it's quoting a frequency?

All help, (or suggestions where I can learn what I need to know) is very much appreciated.

Thanks for looking and have a great weekend.

Stephen Watson

SGW100 said:

Hi all,

Firstly let my apologize for being a complete newbie and knowing NOTHING about electronics.

Click to expand...

Then read up on it before you start building thing or you'll probably be dissapointed when they don't work.

SGW100 said:

I want to produce is a device that delivers a 9 volt dc charge to two electrodes at a current of between 0.25 - 3 milliamps.

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A variable resistor in series with a potentiometer will do that if your load has a low voltage drop like an LED, otherwise you'll need a proper little constant current source.

Why do you want to do this anyway?

SGW100 said:

A dial should control the current at steps of 0.25 milliamps.

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A rotary switch with 12 positions (if such a beast exists) and 12 different resistors is what you need.

May I ask again, why?

SGW100 said:

A timer is also required between 1 - 60 minutes.

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A CMOS timer will do that, I've forgotton the part number but I'll look it up if you want.

SGW100 said:

Finally, I've seen on some dc devices (such as tens machines) quote a frequency.

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Whats a "tens machine"?

No DC device should give a frequency for the power supply. DC is continious direct current it doesn't have a frequency, it's impossible. You must be referring to the requency range (bandwidth) of an amplifier or something.

SGW100 said:

Now I understand that an AC device has a frequency as the direction of the current alternates.

Click to expand...

The frequency litterly meanse the frequency the current changes from one direction to another per second, it's measured in Hz.

SGW100 said:

But what does this frequency refer to if it's a dc device?

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You must be mistaken, perhapps you're thinking about those small mains adaptors for powering DC equipment of the mains, in which case it's the input frequency.

SGW100 said:

Or is it's output current alternating if it's quoting a frequency?

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Depends on the device, if it's an inverter then this is probably the case.

Quack "doctors" have these AC and DC "tens machines" that cause small muscle twitches and patients see it happen and think it does something good for them.

Tens Machines

Anthough this is getting totally off topic, TENS stands for Transcutaneous Electrical Nerve Stimulation.

Far from being used by quacks, they are now given out by NHS pain clinics.

You can read a NHS sheet on them here:

**broken link removed**

I think what the poster was asking was what the frequency such devices was refering to. Although I don't know too much about them I think the electrical impulse is 'pulsed' hence, a purlse frequency.

Silicon chip had a tens project last month, best bet woud be to use that, it would do what your describing.

audioguru said:

Quack "doctors" have these AC and DC "tens machines" that cause small muscle twitches and patients see it happen and think it does something good for them.

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I also disagree. These TENS circuits can be very helpful for some conditions.

The research posted is inconclusive:
"However, research trials that have studied the use of TENS machines have provided conflicting results as to how well they work, and how much pain relief they give. Some conclude that they are not effective. Others conclude that they seem to help some people. Further research is needed to clarify their role and effect."

The placebo effect works with many useless remedies for some gullable people.

audioguru said:

The research posted is inconclusive:
"However, research trials that have studied the use of TENS machines have provided conflicting results as to how well they work, and how much pain relief they give. Some conclude that they are not effective. Others conclude that they seem to help some people. Further research is needed to clarify their role and effect."

The placebo effect works with many useless remedies for some gullable people.

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As I Said, For "Some Conditions"

I have a few Tens circuits on my site and a few guys have given Very Favourable Feedback.
I also know of some Acupuncturists that use these devices, in conjunction with the acupuncture. They claim it helps.

Personally, I have never had a need for one of these devices, and I leave it up to individual to decide for themselves.

It is a doctors' get rich quick scheme. Some people believe in and pay for anything.