Frustration

No, a field effect transistor will switch with almost no current into the gate, so their main advantage in switching applications is that they don't load down the driver circuitry.

They have very high impedance inputs. They can be destroyed by static electricity, so the gate shouldn't be allowed to "float," and there's some limitations on the gate that are in the data sheet for the part you are using. The maximum gate voltage for a lot of FETs is on the order of ~10 volts.

A junction transistor is probably fine for your application. They are somewhat more rugged. But unlike FETs they need current limiting into the base or they will overload the 555 or be destroyed themselves. For what you are doing, 1,000 ohms to 5,000 ohms is probably going to work.

Normally you'd calculate what you need based on the gain (Beta) of the transistor. Gain of 100 and that means the base needs 1/100 of the current that the load will impose on the collector - but look at the graphs, since gains are usually stated as minimum/typical/maximum for the part, and they change with temperature, and the amount of load. If you want to calculate it, but you shouldn't need a driver unless the buzzer has a problem.

What kind of buzzer is this anyway? A piezo buzzer doesn't need a lot of power, something like an electromechanical buzzer would draw a lot of current and a 555 probably couldn't drive it directly. Unless it is a bad buzzer (shorted).

A typical piezo buzzer uses from 5-100 milliamps depending on the part, and the 555 should be able to source that with no problem.

from

formatting link
The output of a standard 555 can sink and source current. This means that two devices can be connected to the output so that one is on when the output is low and the other is on when the output is high, the diagram shows two LEDs connected in this way.

The maximum output current is 200mA, this is more than most ICs and it is sufficient to supply many output transducers directly including LEDs (with a resistor in series), low current lamps, piezo transducers, loudspeakers (with a capacitor in series), relay coils (with diode protection) and some small motors (with diode protection). The output voltage does not quite reach 0V and +Vs, especially if a large current is flowing.

To switch larger currents you can connect a transistor.

NOTE!!!

The maximum output current of low power versions of the 555 (such the ICM7555) is much lower: about 20mA with a 9V supply.

Reply to
default
Loading thread data ...

Looks to me like R1 is missing entirely, and pin 8 looks like it is going to ground when it should go to V+

What is the value of R2? I'm not familiar with that color code. Brn, Gry, Blk, Blk, Brn?

Reply to
default

If you can light a LED, you should be able to make noise with a piezo buzze r.

Your piezo may only be a speaker that also needs an oscillator to make a to ne. Does it make a click when you wire it directly to a battery in either direction? Or, when you put it on your ohm meter, does it initially show some conductance but slowly shows as higher resistance?

If it is a sound maker, you may have it wired backwards. Or it may be dead (not likely). If it is working, it should make noise when you wire it dir ectly to a battery with the correct polarity.

Reply to
jfeng

Pin 8 is going to Vcc.

R2 is 220 ohms.

Reply to
AK

This is the buzzer.

MODEL NO.

7P3120LFLA OPERATING VOLTAGE RANGE ( VDC ) 3 ~ 15 RATED VOLTAGE ( VDC ) 12 ( mA ) 10 ( dBA/ 30 cm ) 90
  • MAX. RATED CURRENT
  • MIN. SOUND OUTPUT
  • FREQUENCY ( Hz ) TONE NATURE PULSE OPERATING TEMPERATURE ( o C ) TERMINAL

- 20 ~ +60 LEADWIRE

The buzzer beeps rather than buzzes. Maybe that is why it will not work in my circuit.

for my ne 555 max output current is +/- 200 ma.

Reply to
AK

Sign is inverted.

Could use a bipolar or mosfet.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
 Click to see the full signature
Reply to
John Larkin

zer.

tone. Does it make a click when you wire it directly to a battery in eith er direction? Or, when you put it on your ohm meter, does it initially sho w some conductance but slowly shows as higher resistance?

ad (not likely). If it is working, it should make noise when you wire it d irectly to a battery with the correct polarity.

I disconnected led and substituted the buzzer.

It does beep but at a fast rate compared to what it sounds when connected d irectly to battery.

Andy

Andy

Reply to
AK

Well, that piezo beeper should to work just fine. Only 10 milliamps when you have 200 available.

You do know LEDs can't connect to power directly, and require some current limiting? This isn't by chance the automobile lamp you referred to as a LED in an earlier post is it? - It may draw some serious current compared to what a 555 outputs.

Most single 5mm LEDs are rated at 20 milliamps maximum and (these days) very bright with 20 ma going through them. I've been limiting currents to one milliamp when I just want a board mounted indicator. The little suckers keep getting more efficient - in the 70's it was hard to tell if they were on with just 20 ma...

But like someone already suggested, connect the buzzer to your power supply to check it's operation. You could also measure the current it uses (with the meter in series with the buzzer and PS)

You can't put the meter across a power supply when using the current functions. That kills the fuse inside the meter or the meter. (so don't do it unless you understand what you are doing)

Reply to
default

R1 is not visible.

Reply to
default

+1
Reply to
Cursitor Doom

I know about current limiting resistors for leds. I am using a 12 v one that has a resistor already soldered into the led.

I wonder why the pulse type piezo buzzer is acting funny.

I checked it's current and it jumps up and down.

Guess that is because it is pulsing?

Andy

Andy

Reply to
AK

Grin, well that's typical for me. I use circuits to check my math. To AK if you build that the output will be low when the light is on. You can just switch the inputs around.

George H.

Reply to
George Herold

Yup, it uses more power to make noise.

Reply to
default

Thanks.

I will order a regular piezo buzzer.

Reply to
AK

The volume is too high on all the buzzers I have seen.

I do not want it bugging my neighbors if I am not at home.

Can I use a pot to turn down the volume?

Andy

Reply to
AK

I had one engineer who absolutely couldn't tell left from right, and also couldn't tell logic "0" from logic "1".

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
 Click to see the full signature
Reply to
John Larkin

I just realized some complications of my project.

I want it to notify me when someone crosses the laser path.

I plan on having the switch,led, and buzzer in my apartment

while the rest is outside in a water resistance project box.

But that means I will need wires going from outside to inside.

And I need to figure where to put the photocell so someone does not trip over it etc.

formatting link

formatting link

Would a motion detector or body heat detector be less complicated?

Andy

Reply to
AK

Less complicated if you buy it ready made, but probably more false alarms. They are better indoors where there are no pets. They respond to light, even if it is a wavelength that you can't see. If you have, for instance, a place that is heated by the sun and a plant/tree branch that moves in the wind it can give a false positive.

They do sell a combination PIR and "radar" (RF field disturbance) detector where both must detect something at the same time to cut down on false alarms.

Passing cars will often trip those from up to ~30 feet away if you are aiming towards a busy street or nearby driveway.

PIR detectors can also detect people moving through widows both open and to a lessor extent closed ones.

There's no good way to predict how well it might work unless you have some prior experience and develop a feel for the application. Then too, how concerned are you with false alarms?

Most of the garden variety of PIR detectors have a wide field of coverage, but you can apply baffles to narrow the field, or find one that has a narrow field - usually combined with greater detection range. Only way to tell is to get one and play with it.

I was fooling around with an RF field disturbance sensor at work and it did a pretty good job of alerting me to people walking by my office/workshop. I just taped it to the wall board inside my office. The range wasn't fantastic but it did not alert when someone moved around in a nearby office. I suspect it may have alarmed if someone in a nearby office was moving something metal around - it was more sensitive to metal objects than people.

I did make a visible light movement detector. I used two photocells and a lens along with some op-amps to detect changes in one photocell that didn't match the other - so it could ignore switching on lights or the sun rising, but still detect movement. (same principle as PIR detectors but works in lighted areas only)

I was trying to find a way to protect people from walking into moving machinery without a physical barrier. We went with a physical barrier that required the operator to look inside the cage before he pressed the "start" button. Nothing else was as foolproof.

Reply to
default

To some extent you can. But most of them are a piezo ceramic disk that has two driving electrodes plated on the sides along with a third electrode that provides electrical feedback to make it oscillate at it's natural resonant frequency. That is most efficient and produces the most volume for the least power.

If you turn the voltage down too low, it won't be able to oscillate.

You could make a 555 into an astable multivibrator and drive a small speaker or piezo transducer and add a pot to change the volume from nothing to maximum. I'd bet there's some schematic like that on-line already.

You could control pitch and volume and with a speaker it might even sound better.

With a speaker you need a cap in series with it to just pass the AC to the speaker. A piezo transducer is a capacitor.

Or you might just be able to block the opening for the buzzer to attenuate the sound.

(like painting LEDs to reduce the intensity - the easy way out - "put a sock in it.")

Reply to
default

Given a few minutes I can get right and left. As navigator in a car I'll use 'towards you' or 'towards me', which I'm less likely to mix up.

As far as logic goes, well sometimes high is a '0' and sometimes it's a '1'. So I sympathize with your engineer.

George H.

Reply to
George Herold

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.