Four Wave Mixing

[Shanjaq]

50 ohms and heating

The image is cut off on the left side. where it says "50" it really means "150". Reading documentation on using the 555 timer IC, NO LESS THAN 100 OHMS should be present between the Discharge pin and VCC (7 and 8 for most pinouts.)

Hope this helps.

[blackchisel97]

The image is cut off on the left side. where it says "50" it really means "150". Reading documentation on using the 555 timer IC, NO LESS THAN 100 OHMS should be present between the Discharge pin and VCC (7 and 8 for most pinouts.)

Hope this helps.

Yes I did replace them right away for 120 and later 150 but this is still low value. Those resistors are .25W and get hot. Oscillator draws nearly 60mA instead of 5-7mA. Is there a reason for that? Just wondering.
If all oscillators would operate at 5-7mA each, the entire device would draw between 40-50mA at max. Not 350mA. I'll put this back on the bench once I'm done with other projects.

Thanks
Vtech

[Mostie]

The image is cut off on the left side. where it says "50" it really means "150". Reading documentation on using the 555 timer IC, NO LESS THAN 100 OHMS should be present between the Discharge pin and VCC (7 and 8 for most pinouts.)

Hope this helps.

not really, if you read post 1 by JB, he gives you the value's ????

BC, got the first 2 working with 1K resistors, changed the cap on no.2.

[blackchisel97]

Thanks Mostie. Even with lower resistance such as 680 Ohms as per other oscillators it will work fine. Mine 555's are not cmos, as recommended by John. Beside datasheet, if you look at internal schematic of 555, 50 or even 100 Ohms is too low for IC to operate.Caps can be adjusted accordingly to obtain right pulse rate and d.c.
I would love to hear a word or two from John. Unless, for some reasons he prefers not to touch this subject, which I can understand. At the same time I have no problem replicating and sharing my results with any device, as long as I know what I'm doing right or wrong.

Vtech

[Shanjaq]

not really, if you read post 1 by JB, he gives you the value's ????

Read your 555 datasheet, specifically the Absolute Maximum Ratings for Power Dissipation. I won't speculate on JB's quote, but this is just how it is: Your timer will soon die if you put less than 100 ohms between VCC and Discharge pin.

[Mostie]

Read your 555 datasheet, specifically the Absolute Maximum Ratings for Power Dissipation. I won't speculate on JB's quote, but this is just how it is: Your timer will soon die if you put less than 100 ohms between VCC and Discharge pin.

that wasn't my point, you were trying to imply the values had been cut by the copier, when JB states these as being correct, however if you read my previous posts to BC, I already knew there was a problem and started to change them.

[blackchisel97]

My 2 pennies:
I think we can adjust the resistance in order to stay on the pulse rate according to the schematic and comply with manufacturer specs. As I stated before, 100 Ohm is an absolute minimum to get oscillator working (tried) but it results in unnecessary heating of IC and resistor. Anywhere from 560 Ohm - 1k is fine. Actually, I would prefer 1k. With such value oscillator draws only 5-6mA and there is no strain on components.

Vtech

[Mostie]

Hello BC, 1k is what I'm aiming for, just play with the 555 calculator until you get a decent duty cycle. what do you think about the freq. of osc 4&5?

[blackchisel97]

Hello BC, 1k is what I'm aiming for, just play with the 555 calculator until you get a decent duty cycle. what do you think about the freq. of osc 4&5?

Hi Mostie.

I listed pulse rates which I arrived with in post 140. Oscillators with fixed resistors were calculated and they are pretty close in working device. If I remember well I've got near 800pps and 7,500pps in 4&5, 20,000pps in 6th and 7pps in 7th. I had to change cap in 7th since I couldn't adjust to 7pps with circuit value.

Vtech

[blackchisel97]

Hey BC,
So are you suggesting that we should use 1k Ohms resistors between pin 8 and 7 of the 555s?

Well, I can't really suggest anything to anyone but I would like to get this device working properly.
Since we know the pulse rates of each oscillator as well as their duty cycle - 50% that is the goal. I don't understand the purpose of pumping more mA into 555 by lowering the resistance to the treshold. I just noticed that my solderless proto board (plastic) got slightly melted under the first chip running at first with 120 Ohm, before I replaced with 150. That was absolute minimum in order to make it work at all.
500 - 600, or 680 Ohms will do but 1k is quite common and will help us to compare data.

Thanks
Vtech

[Prinsloo]

Hi guys

Was trying to play catch-up on this thread, good work, VERY GOOD work you guys, sorry but time and bucks are few so have to salt mine to keep staying floating.

My 2c worth, I have read a page some time ago of different manufactures 555 chips have different characteristics that have very different effects on circuit design, maybe a good thing to look into this as well, Maybe TomC and others will be so kind and tel us the manufacturers of the 555 they are using and compare notes . . . .

A year ago I have build a multiple timer circuit for an alarm system with multiple inputs on different circuits, using 11 x 555 timers ( I know a PIC would have been better) and after many an hour of frustration and tears, discovered what the problem was, in the design process I fried 2 of the 555 IC's from the original batch and replaced them with IC's from my spares box, (different manufacturer than the rest) and could not get it working properly until I replaced them with the same (manufacturer and bought them from the same store) as the originals, might sound nuts to some but this is what I experienced.

Just a thought,

Theunis

[Mostie]

Theunis, I thought the same thing about the 555's, however I assumed they were a generic design.
I think JB used TI, mine are all ST, might be useful know what other folks have used.

[blackchisel97]

Mine are ST. I think, just for giggles I'll make another replication but this time using HCF4047. I tried them in my Red Light Pulser and I like it. They hold 50% d.c and can be tuned precisely by resistance only. I can cover all 7 settings from 73Hz to 4,672Hz using same 10n cap. Their cost is the same as 555. They have 14 pins and require same amount of other components.
Just need to wrap few other projects first.

Thanks
Vtech

[Prinsloo]

I also though about that Vtech, they are also more stable and don't float as much as 555.

Theunis

[blackchisel97]

Well, we're on the same page Theunis. I'm expecting courier with precise frequency meter and RF signal generator for up to 450Mhz within a day. My digital signal gen. is precise down to 4 decimals but when it reads external source it automatically cuts the reading. 1168Hz reads as 1.16kHz and doesn't give a clue about the next decimal. I need this to wrap my Light Therapy project. Everything else works fine and it should be nice looking/working unit when done.
I was also thinking of running Dr Beck Tuner on those chips instead of 555 and 556. Transistor part could be substituted with op amp but since it works fine I'm not motivated enough to fiddle with. If ain't broken don't try to fix it.

Thanks
Vtech