Author Options:

I need help setting up a 2Mhz oscillator circuit Answered

So here's the backstory : Last night I was poking around in our shed looking for ..... when I came across a box of old electronics. Inside was a lot of old parts, from about the 1970's, a few 555's and 741's and a big 28 pin chip I didn't recognize. After plugging the numbers on the chip into google (AY-3-8500) I found out that it was freaking pong on a chip. Apparently my dad had bought it as a kit in the 70's but never got around to make it.
So I took a look around the net for schematics and found

Here's the problem, I don't have easy access to the 90uH inductor in the schematics or a 2Mhz crystal.

So how can I create the 2Mhz I need to run the chip? It's the only thing between me and pong X(


UPDATE: Everything works, no idea why Ok I have the paddles working but I have no idea why they work. Working off the datasheet diagram instead of hooking pot pin 1 to the 10k Ohm resistor, hook it between Vss and the 0.1uF cap, pin 2 connects to pin 3 and pin 3 connects to between the 0.1uF cap and the 10k Ohm resistor, instead of to Vcc. I'm happy that I have pong working but a little annoyed that I have no idea why. Thanks to everyone that helped, especially you gmoon.

One small problem, the bats are a little glitchy and oscillate up and down every 5 or so second, it wouldn't be a problem if the oscillations were small but they are about 1/3 of the screen :S Any ideas?

Hah, so everything works now, except only the ball is displayed on the screen, I should be able to fix that by playing around with the 4071 chip.

Cool. Great to see the next gen resurrect a project Dad never finished (I broke more of my Dad's stuff than I fixed...) I'm sure those logic gates matter.

Haha, yeah me too :P The ball, scoring and feild are all operational now, just having a bit of a problem with the damn paddles (kind on essential :P)

Ok, Here's an interesting twist, If I connect either side of the 0.1uF caps in the right and left paddle circuits the paddles display on the screen (somewhat glitchily, but they are there). I tried shorting the cap and that doesn't work either (well sort of, but I have to be touching the 220 Ohm resistor instead of the cap ><). I was thinking the pots are too big, but I'm using 1M ohm pots like in the diagram. Any suggestions?

So I went and did some work before coming back to ask another question: A 4Mhz crystal and a 4017 decade counter chip should work if I: Connect the crystal to the "clock" pin of the 4017, connect Q2 to the rest pin of the 4017 and also to the clock input pin of the Ay-3-8500 This means that every 2nd high that goes into the 4017 will output a high and reset the 4017, halving the 4Mhz down to 2Mhz. Oh and I'd run it at 6v since the datasheet says the 4017 tops at 2Mhz at 5v, it should be a bit higher at 6v, just to be safe Am I right? or am I just an idiot going down the wrong path? (thanks for all the help so far too :D, it'll be pong time in no time)

There's an "Alternate 2mHz Osc." speced out on the PDF you provided. It uses a 2mHz crystal and two CMOS gates (4001 or 4011), along with a few other components.

Oh, I see you've already rejected the 2mHz Xtal.... (they really aren't hard to find.)

I found a nearby source for the 2Mhz (finally :P), why does the schematic say 4011 but have a NOR picture? I think they are both meant to be NOR

and also, if (in the alternate circuit for the 2Mhz crystal) 4 goes to the clock input, where does the circuit connect to Vss?

The PDF specs either a 4001 or a 4011. The NOR gates are the 4001; the same connections would work with the NAND gates of a 4011 (the pulse might be the opposite phase, but that won't matter.) They chose to draw only one type of gate... You probably should ground any unused CMOS inputs... It's common to leave out the GND and Vcc pin connections on a schematic, particularly when the chip is common, and is draw in a conceptual manner--the individual gates, rather than a monolithic block. Find that info on the 4001 or 4011 datasheet and connect power pins as required.

I love you gmoon, I think I have all the parts now, except for the 4073, I have a 4071 instead which should substitute (if pinned correctly) and a 4001. I'll post back after my first trial

most likely it'll work perfectly on any lower clock. few tens / hundreds KHz are enough for lots of stuff

Buy the crystal & the inductor ;-)

Its highly likely to work, and chances are you won't be able to solve this problem without buying something...

I'd have to order the parts from the net and I would be pongless for days while I wait for delivery. I know I'll have to buy something but I was hoping it would be something more widely available :P

Weeelll, my days are pretty booked going up to christmas, but tomorrow is free for me. I can get my hands on a 4 Mhz crystal and a 4017 divider, anyone know if that would work?

I'm too tired to check (btw noone helped me on my led driver as of recently, thanks!), but that should work if the 4017 can handle that speed.

I would have helped but I don't reaaalllly know that much about electronics (I can follow a diagram pretty well though :P)

all of a sudden i got less lazy, the 4017 might work, but your pushing it to the max. at 5 volts it's maximum clock frequency is 2MHz It's not that I can't do the math for my led driver, it's just that I'm too tired (have had barley any sleep for 5 days now, feel like I'm going to pass out... ahhhhhh