Trying to figure out this schematic i want to build - Page 1
Forum section: electronics / projects

author: cao20581
author_rank: Newbie
timestamp: September 29, 2014, 06:32:52 am
content: Hi,im new to this forum and Im somewhat familiar with electronic circuits but having some problems trying out a project i want to build.(gonna try to attach the schematic and picture of the board in this message) The issue with this schematic is that i have no clue what the resistor/capacitor/diode values are from reading it as its not clear cut on what everything is. Do you think its possible to build this with the schematic the way it is? Can anyone offer there time to fix it and redraw correctly? If i had money i'd pay you but wont have anything until next month. I really want to build it but i just dont know if its even worth my time.thanks

author: rexxar
author_rank: Frequent Contributor
timestamp: September 29, 2014, 07:26:39 am
content: All of the caps with a + mark next to them are electrolytic. The + indicates the polarity in the circuit. The others are most likely ceramic. Looks like the circuit is 5V, so use caps rated at 10V or higher. It looks like all the parts are labelled, though not in a really intuitive way.This schematic is drawn out kind of strange, I don't blame you for not being able to follow it. Youcanbuild the circuit from this schematic, but it'll give you a headache. Personally, I'd clean it up a bit first-- for sanity's sake.I'll see if I have time to play with the schematic after class tomorrow

author: cao20581
author_rank: Newbie
timestamp: September 29, 2014, 06:30:23 pm
content: That was the main thing that got me was trying to figure out the values for each.Seemed damn near impossible, But i only know so much about electronics. If you can fix it up to actually make it a usable schematic i would appreciate it.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 29, 2014, 06:53:24 pm
content: There is nothing grossly wrong with the schematic diagram as-is. Yes, it is rather rough around the edges, but still perfectly readable.I don't see anything that isn't properly labeled, although the inductors are drawn with a weird symbol which I have not seen before.The legibility of the schematic diagram is the least of your concerns. That appears to be rather an old design.Both of the crucial parts of the design, theTDA7088Tchip for FM receiver, as well as theMK484chip for AM receiver are bothOBSOLETEand hard to find (read: "expensive").And they weren't all that available even before they went obsolete.Do you already have these chips? If not, you might want to acquire them before proceeding any further. It may be a moot point.Those 555 timer chips for "Reset" and "Scan" seem odd. Do you know what this circuit is supposed to do?It isn't obvious upon cursory glance at the schematic diagram.

author: cao20581
author_rank: Newbie
timestamp: September 29, 2014, 08:15:33 pm
content: I unfortunately don't have those chips and was hoping to find maybe some older radios that might have them. The circuit is a original "ghost box" that uses radio signals to have the spirits speak through or whatever. So basically a radio that scan through the stations unstopped.The original schematic came from a 'Joe's box' and he passed away but always uploaded the schematics for other people to build.That's pretty much all the schematic and picture of the circuit i got to show.Any idea where i might purchase those chips just to get an idea of how expensive it would be?

author: SeanB
author_rank: Super Contributor
timestamp: September 29, 2014, 08:36:20 pm
content: You could do the same using a cheap FM radio, just using the 2 555 timers and the RC circuit to drive a varicap capacitor replacing the original tuning capacitors. It basically just uses the one 555 to emulate the pressing of the pushbuttons on a cheap FM scanning radio ( look in the cheap radios for a radio with 2 pushbuttons for scan and reset to get it all in a single unit that has the complete FM side in a blob) and the varicap does the same for the AM side. the second one resets the tuning at a random time so you only tune through a select part of the band.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 29, 2014, 09:34:49 pm
content: Unless you get really lucky, I would rate your chances of finding these chips extremely low.And your chance of finding and recycling them out of old radios even lower.There are modern equivalents of radio receiver chips, but they are virtually all digitally controlled.For example these...https://www.sparkfun.com/products/10663https://www.sparkfun.com/products/11737You lost me with the "spirits speaking" stuff. We must assume you are joking.

author: cao20581
author_rank: Newbie
timestamp: September 30, 2014, 12:21:49 am
content: It's paranormal researchSome people believe it in,while others don't...I'm still open for figuring it out on my own if its true.idk.Regardless of its purpose i wanted it to be my first project to work on. For me the circuit is still hard to read. Can someone clear it up enough to where i could understand it? I know everyone here has years and years experience with this and yet maybe a few months for me.Thanks for the idea SeanB. that could definitely be another one for me to try.And thanks for those other chips Richard.I still need to work my way upto figuring how to replace those with the other one. I found the TDA7088T chip for sale:http://www.futurlec.com/Philips/TDA7088Tpr.shtmlIs it not the right one i would need for this circuit?

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 30, 2014, 01:29:05 am
content: Yes, that is the chip. I had a sneaking suspicion that Futurlec might still list it. Unfortunately, Futurelec has a terrible reputation for customer service. So they may not actually have any even thought they are listed on their website. I believe there was a newer chip that was similar to the MK484, but I don't remember what it was called.You keep saying that the schematic is confusing to read, but I don't know what re-drawing it would improve? What exactly are you having trouble with? Maybe we can help you read what you already have.

author: cao20581
author_rank: Newbie
timestamp: September 30, 2014, 01:51:58 am
content: I think for me i just looks different from a standard schematic. Im still learning how to read them but i cant really understand the capacitor/resistor/diode values and a few other things.(like where it says 100n capacitor?) ill circle the things i need help with and hopefully you can come up with a list of what i might need to get. You dont have to do all of them but im just trying to figure out a general idea of what i might need and how its setup.thanks

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 30, 2014, 03:56:52 am
content: I have added component reference numbers to the schematic diagram.Posted here:http://www.rcrowley.com/images/SpookRec.pngAnd here is the list of components. There are a couple which are undefined:C10 is not defined. It is probably something between 10 pF and 100 pF. Perhaps the TDA7088T data sheet would be helpful.D3 is undefined. You will need to find a diode by matching the specifications.It says it wants a capacitance range of 10-100 pF over some unspecified voltage range.R1 1M ohm control potR2 100K ohm resistorR3 10K ohm resistorR4 100K ohm trim-potR5 100K ohm resistorR6 10K ohm resistorR7 1M ohm control potR8 100K ohm resistorR9 10K ohm resistorR10 100K trim-potR11 100K ohm resistorR12 10K ohm resistorR13 10K ohm resistorR14 10K ohm resistorR15 1K ohm resistorR16 10K ohm resistorR17 22K ohm resistorR18 10K ohm resistorR19 1K ohm resistorR20 1K ohm resistorR21 10 ohm resistorR22 100K ohm resistorR23 100K ohm resistorR24 680 ohm resistorR25 10K ohm resistorC1 0.1 uF capacitorC2 10uF capacitorC3 0.1uF capacitorC4 0.1uF capacitorC5 1 uF capacitorC6 100 nF capacitorC7 470 pF capacitorC8 50 pF capacitorC9 80 pF capacitorC10 unlabeled?C11 100 nF capacitorC12 22 nF capacitorC13 180 pF capacitorC14 330 pF capacitorC15 100 nF capacitorC16 1000 uF capacitorC17 10 nF capacitorC18 3.9 nF capacitorC19 4.7 nF capacitorC20 4.7 nF capacitorC21 10 nF capacitorC22 100 uF capacitorC23 470 pF capacitorC24 220 uF capacitorC25 10 nF capacitorC26 100 nF capacitorC27 0.1 uF capacitorC28 1 uF capacitorC29 680 pF capacitorCapacitors that are 1uF and higher are electrolytic, and those below that are whatever is expedient.Since the power supply voltage is 5V, then you don't need voltage ratings any higher than 10V for the electrolytics.U1 TLC555 timer IC (period)U2 TLC555 timer IC (rate)U3 TDA7088T FM receiver ICU4 MK484 AM receiver ICU5 LM386 audio amplifier ICD1 1N4001 diodeD2 BB-909-B varactor diodeD3? (10-100pF varactor)Q1 2N3906 transistorQ2 2N3906 transistorQ3 2N3906 transistor

author: cao20581
author_rank: Newbie
timestamp: September 30, 2014, 04:08:44 am
content: WOW! Thank you so much Richard! I didn't expect all that but im really gratefulHave no clue how you did that so fast but that's amazing. That really gets me a lot farther into building it than i would have ever gotten.lol. I will do some research on the missing ones and see if i can come up with the right value from the data sheet. Cant say thank you enough

author: Unknown
author_rank: Unknown
timestamp: September 30, 2014, 09:23:45 am
content: Quote from: Richard Crowley on September 30, 2014, 03:56:52 amQuote from: cao20581 on September 30, 2014, 04:08:44 amI've seen far too many circuits for these things (a natural result of trying to google info on low voltage &/or high Cr high-capacitance varicaps). That's a pretty standard circuit and, as far as I've seen, they're all very vague on an actual part number for that varicap. I suspect no one's ever built one - at least, not one that works properly (whatever 'properly' means in ghosthunter/spiritualist terms...).FWIW, a 'normal' ZN/MK414 circuit typically uses something like a BB201 or similar there. With a 5v supply that'd give an adjustment range of ~40-100pF which, with the 600uH L3 (loopstick antenna?) & associated components, is about right to tune across the AM BC band. One slight issue is the BB201 is a dual-diode varicap, so I suspect the Ur-original of these 'ghost boxes' used a single diode varicap that was discontinued long ago, and no-one playing with them has enough actual electronics knowledge to choose a substitute.It'd be easy to substitute a BB201 (which IIRC is still manufactured by NXP); simply follow the typical ZN414 circuit and connect it in place with the control voltage to the common cathodes in the middle. If you really want 10-100pF you could probably use something like an NTE618 in parallel with a fixed 100pF or thereabouts.

author: dexters_lab
author_rank: Unknown
timestamp: September 30, 2014, 01:03:23 pm
content: from what i know of this subject many ghost boxes can be created by modifying existing portable fm radios so they just continually scan the fm radio bandunless your just 'up for the challenge' then modding one might be a better option?

author: cao20581
author_rank: Newbie
timestamp: September 30, 2014, 04:37:23 pm
content: I forgot to mention but the guy that built the design for this radio was electrical engineer, which i guess explains its complexity. There are still some of his boxes around, and i really only have the desire to build this one. I think with Richards help we have come along way to figuring it out, and i know i still have a lot more to learn before i'll actually make it. I really just want to build it exact to the schematic if possible.