Driver Circuit For 280Zx Dinger

[TomoHawk]

Here's one for Cap'N O-

 

I have a dinger from a 280ZX, but it doesn't ding-dong all by itself.  It's basically a tiny doorbell, so it only goes ding-dong if you pulse the electric power.

 

My goal is to power it, like you would a small bulb flasher.  There is to be a minimum of parts (2 or 3.)  My two ideas so far were to use a blinking Christmas tree bulb (Circuit 1) and just run the 12V through it.  It should work, but the ding-dong rate should be a little slow.  The other idea uses a flashing LED (Circuit 2) to control a transistor, so the bell gets enough current.

 

I had some graphics prepared, but I'm still figuring out how to get one into a message.

 

 

 

 

 

 

 

[Captain Obvious]

The blinking Christmas tree bulb would be a very easy (and IMHO elegant) solution, but you'd have to make sure the bulb was designed to flash on the current drawn by the ding-dong. If it's not enough current, you could add a resistor in parallel with the ding-dong to supplement the draw, but if it's already too much, you're out of luck.

 

The other circuit based on the Esaki effect on the transistor worries me a little. I'm not sure how many times a back biased junction that was never designed to be used as a Zener would fare over time. Maybe because the power in the whole thing is so limited it wouldn't be a problem, but I just wonder if the transistor could take it forever.

 

Also, I'm not sure if the dump pulse would be long enough to get your ding-dong to ding. The ding-dong is driven by a coil (an inductor) which means that not only will resist the current dump, but it also takes a certain duration to establish enough of a field to swing the movable pole to ding before it springs back to dong.

 

How about a turn signal flasher? Might not work because the ding-ding doesn't draw enough current (same potential issue as using the xmas light bulb), but one of them new fangled flashers for use with LED's should work.

 

Just tossing out possible alternatives?

[Captain Obvious]

Another alternative? The dimmer circuit knob on all the Honda Civics uses the ubiquitous astable multivibrator. You know... this one that's used absolutely everywhere:

 

I've already harvested them for other applications. Change a couple passive component values and you should be able to tune it for whatever frequency and duty cycle sounds good.

 

Not only that, but it comes with it's own build in pot for tuning on the fly. 

 

[TomoHawk]

Thanks Cap'n O

 

I'd have to make a PCB for the multivibrator, but I could include a trimpot. The blinky light  would be glued right to the case. I will see if the CVS still has them on Saturday.

 

for the second idea, the transistor would only need to take it for a few seconds, because the dinger is for the headlamp warning, and arse soon as you hear it, you need to turn of the headlamps or close the door.

 

BTW- the dinger is from a new Hyundai, but it's the same thing, two metal bars that are tapped by a solenoid hammer.

[Captain Obvious]

You wouldn't have to do any PCB work for the Civic dimmer. The beauty of it is that it's already pre-packaged in a little module. PCB inside already and knob for adjusting the duty cycle. I reverse engineered the circuit so that's how I know what's inside. All you would have to do is change some of the passives to tune it to a more reasonable frequency (it's currently way too high because they don't want the incandescent lamps flickering) and maybe adjust the duty cycle as well.

 

It's pretty small... Maybe inch by inch-n-a-half? I've got one in a box somewhere around here. I'll dig it out and snap a pic or two to show you what I'm talking about.

 

Last time I used one I took just the PCB out of the plastic housing and replaced the brightness knob pot with a fixed resistor and wrapped the result in electrical tape instead of using the plastic housing. Gets way smaller when you do that. End result is maybe half inch by one inch? Glue that to the top of your ding-dong.

 

A dollar at the junkyard. I couldn't build one from scratch for that.
 

[TomoHawk]

Now I'm confused.   All I really need is to get a square wave of 12V, with a bit of current.  Could you get it to flip-flop slowly enough?  (1Hz)

[Captain Obvious]

In it's original configuration (with the original values as supplied by Honda) it flip-flops much faster than 1Hz. But the point is that by changing a couple resistor values and maybe the caps, you can configure it for whatever frequency you desire. And yes, 1Hz is easily achievable. Also in it's typical configuration, it's setup for 50/50 duty cycle, but by using different resistors on each side (instead of the same values on both sides), you can imbalance the charging rates and change the duty cycle as well.

 

There's lots of info on the web, but here's one site that also includes a some scope photos and videos.

http://rayshobby.net/?p=1079

 

Been a long time since I was messing with the module, but I believe there is also one additional "output driver" transistor hanging off one of the collectors so the bulb current doesn't go through either of the oscillator transistors. I have to find my notes... I took a quick look and couldn't find them, but hopefully in the light of day tomorrow they'll turn up.

 

I'm envisioning this:

Pull a dimmer module from a Civic.

Pop the circuit PCB out of the plastic shell.

Change a couple resistor values and maybe the caps to get an appropriate frequency and a pleasant sounding duty-cycle.

(For example, maybe 1Hz and 70/30 duty cycle for ding..dong............ding..dong..........ding..dong)

(Or 50/50 duty cycle for ding......dong......ding......dong......ding......dong......)

Run +12 and ground to the module.

Connect the module output to your ding-dong.

 

Pics and notes tomorrow hopefully.

[TomoHawk]

a 70/30 cycle should be fine, but IMO an 80/20 cycle would be better,  long as it starts with the ding.

 

the weird thing is that you see a bunch of circuits on the Internet, with videos of flashing LEDs, but they don't show where the load goes.

[Captain Obvious]

Here's some pics of the kind of stuff I'm thinking about. Here are two modules. 96-00 Civic on the left and something else on the right. Don't remember what... Prelude maybe? Anyway, they're basically the same in the way they work:

 

Pop the cases open and you're looking at the guts:

 

They've already got an output transistor built into the module which is an open collector or open drain and all you need to do is connect one side of your load to +12 and the other side to the output pin of the dimmer module. You can't see it, but the output transistor is a TO-220 device on a heat sink on the other side of the board:

 

The Civic module originally flip-flopped around 100Hz. I took a couple minutes messing around with changing the original component values to change the frequency until I got something roughly around 1Hz and something a little off from 50/50 duty cycle:

 

Finalize the values, solder them into permanent position, wrap with electrical tape (or snap back into the original plastic shell) and hot glue gun to the top of your ding-dong.

 

I'm a little pressed for time right now, but maybe that can get you started?
 

[TomoHawk]

It looks like an idea to try.  Everything except the hot glue-  I use GOOP for that.

[TomoHawk]

here's another idea:

 

This uy added a second transistor to the Esake effect circuit, and "by adding a second transistor to make a latch when combined with the negative-resistance transistor, I could get a brighter, longer flash."

 

http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html

 

 

[Captain Obvious]

Adding that second transistor to elongate the pulse would probably help with driving the armature, but I'm still worried about repeatedly avalanching a junction that was never designed for that. I mean it's cheap and easy enough to just try, but I just don't know what the long term (or temperature) performance would be like.

 

You want me to send you one of the PWM dimmers modified to something that would drive your ding-dong? 

 

BTW - I went digging online for pics and I believe I have identified the other dimmer module in my pic above to be from a Mazda Protégé or 626. Not only is it a little more sophisticated than the Civic dimmer, but it's also more compact even though it's got two output stage driver transistors in parallel (don't know why). One transistor is larger and heatsinked, and the other is a little smaller and is soldered right to the PCB (you can see it in my pic above). I bet for intermittent use, like for your ding-dong, you could get away with the smaller output transistor and could completely remove the other transistor and heat sink to make small like watch.