Introduction: Hacking an Otherwise Dysfunctional Digital Recorder - Finished !

I want to show, not just one way to hack this device and make it more functional, but the process & steps I took to decide how and what parts to improve.

Thus, the $10-$11 investment made become more worthwhile (especially if one takes it "all the way".

So, let's get to making this device worthwhile.

Step 1: Parts / Equipment N Cautions

Of course, one needs to have the circuit pictured in the Intro. It records a very LOW level of sound IF one gets within millimeters of the Speaker, which is also the acting mic.

Whichever "AMP" one wishes to use, or the one I will be building in a subsequent step (meaning the parts for it),

The Amp I constructed used:

One: LM386 audio amp
Three: 10uF polarized capacitors
One: Non-polarized 1 uF capacitor
One: 100 uF polarized capacitor
One: 1 nF ceramic capacitor
One: 47 nF ceramic capacitor
One: slide 10K pot; three legs
One: socket, for AMP
One: 8 ohm 4 ohm speaker

A DPDT switch ( instead of having the mic draw power all the time, since output was already weak, I install a switch ), or 2 SPST switches.

and of course solder, soldering iron, eye protection, and caution working around the equipment.

The Amp schematics I used can be found here: Audio Amplifiers / simple LM386 Audio Amp and is similar to the one below, but not exactly the same.

Step 2: A Beginning. . .

When I got this "digital voice recorder" originally it was to use for my April Fools instructable. But it's recording capabilities were Nearly non-existent, and playback was impossibly low in volume.

My first thought was that, since the Mic and the speaker were the same (this can be done, but as we see, with poor results), I decided to add my own Mic.

But, after testing it, I found the sound only slightly improved. So once again, I decided to take some of the power users out of the equation and installed a switch in line with the Mic (had I had a better switch, I could have wired it as an on / off - off / on; that is, on for mic off for speaker OR on for speaker off for mic).

This too improved the quality of the recording, but not the volume. I was beginning to wonder if it was the chip and I would then have to give up on it for now. The chip I used 20 years or so ago, was not available from RS as they did not get much business anymore for "parts" of that sort.

Ok, well there is always amplification :-)

Step 3: The Pre-amp / Amp

In putting this together, I ran into a little difficulty locally finding a 10 ohm resistor. But, once acquired (yesterday - today's date is on the photo), it was pretty easy to finish up most of the way.
I have all the components in and it is ready for setting up and testing.

When I feel up to it, I will wire it all together and give it a go. First, I want to test it on the "back end", that is, as an amp for the meager output of the DVR/P chip.

I do believe, from my early experiments in attempting to up the volume input, that the chip was unable to handle the higher volume, so it would probably be a waste of time trying to up the volume being recorded.

Step 4: Final Revisions

I finally got the speaker off the RS device, and put the amp (gain of approximately 200) in between.

The first test shows me it worked, in a limited sense. The volume is way up, and I can actually hear the output, however there is a bit of distortion and maybe some clipping going on that I will have to tweak out later. I may need a better matched or more sensitive mic.

For now, this is a step in the right direction, and only (I hope) needs a bit of tweaking to be added as I have time.

I will publish this however as it is along overdue.

Step 5: The Pre-Amp

Although the amplification is good, the output is still quite rough.

Before trying to alter the circuit I have already installed, I thought I should try to clean up the input, since it was originally getting it from a speaker as a mic.

I added a pre-amp to help drive the mic's signal. This helped some again, but I still need to compensate for what sounds like a bit of overdriving the speaker.

I think I will try to find a better speaker and see if that doesn't help some.

Step 6: Couldn't Find a Suitable Speaker (I Have One, I Just Can't Find It at This Time :-)

So, just for grins and giggles, I replaced the Mic (it was a small "crystal" mic, I found out, and needed a bit more "drive" than even the pre-amp could supply).

It sounds a WHOLE lot better now. The speaker will make a big difference too, once I come across it. Then I will make it look nice (box it and such), and although it will not be as small as those units you can buy for reminders, this started out as no where near that small a device that was non-functional from new. And now it has function :-)

Step 7: And Now for a Change of Speaker

Below is the speaker and assembly I will install next, to see of the impedance response is better (better matched).

The voice quality was improved tremendously. Shunting the output with a .5uF non-polarized cap also seemed to smooth out some of the clipping that was coming from the 200X amp.

Step 8: Putting the Speaker Back Where It Belonged....

I was having a real Dickens of a time trying to find a suitable "container" or box for this project...then I realized that the enclosure that originally held the speaker I used, a small tower of plastic for what was 1/2 of a computer speaker pair, would work perfectly.

My only problem will be in incorporating a way to adjust the slider switch (volume), which I have soldered to the PC board. This may be a bit tricky. Here are some pictures to show where I am going with this:

Step 9: S.M. Buttons and Other Problems....

Handling the surface mount buttons, the 2 switches, and the PC board mounted sliding volume control are my last problems as well as finding a "place" for the battery.

I mounted the "speaker / mic" switch directly behind the ( record / play) board at the top of the mechanism. The "power, on / off" switch is just left of that (both out of view of these pictures).

I was having diffulties working with the plastic of this case, so I didn't have an elegant answer as to how to mount the board mounted push buttons. They are hot glued (for now) to the top of the speaker cabinet.

The second picture shows the slot access to the slider volume control. I need to arrange for a way to adjust that yet too.

More then likely, this whole project could have been 10 times easier if I had just used the components of the speaker (internal amp, volume controls, etc) BUT it would have two things against it.
#1: it would need a 12 vdc power source (transformer)
#2: I haven't built an AMP from the ground up for nearly 20 years, and I needed the practice :-)

Step 10: Finishing Up

Here is the final product. It is still a little crude, but I haven't the resources I once had.

Especially crude is the battery holder. I had nothing else in the house that would work as well. The Styrofoam was available.

The non-functioning boards are there for two reasons. On to help hide some of the wiring and the fact that the small "original" board (with the red LED on it) overhung the top a bit.

Adding the LED was difficult, as the tiny red one was so close to the board. First I had to determine which lead was the anode and which the cathode. An analog multimeter I had handy determined that fairly quickly (after I got 20 seconds of collaboration from my wife ;-).

I tinned my iron tip (so it had a little solder on it and would draw any from the board), touched the joint for a second or two, and pulled back, creating a small "peak". Then I tinned the wire leg of the "added" LED and then soldered it in.

This instructible is more of a "do this with what you can find around the house" kind of project. Except for the AMP, which I had already gotten parts for, everything else was scrounged from my junk box.

Here is how I finally got it to sound:


aeromancy made it!(author)2008-07-21

If only this was posted sooner....I had one of these, but I returned it because it wasn't loud enough. I will most likely go out and purchase another thanks to this great Instructable. Keep up the good work.

Goodhart made it!(author)2008-07-26

I have finished it as best as I can for now. It really needs to be looked at as a "do it your own way" project for the most part. The AMP need not be a 200x either in order to fact, a 10x should do it.

aeromancy made it!(author)2008-07-27

Thanks for the update. When I make this, I will be sure to upload some photos.

Goodhart made it!(author)2008-07-27

Yes, thank you, I would love to see how others take this, and what containers they use and how they overcome that "mounted play button" problem.

ampRiser made it!(author)2009-09-02

Great instrucatable! I did a hack on this same circuit so that I could control the play button with a normally open foot switch. I carefully pried the metal tabs holding the surface mount button in place, so that it could be removed, then I lightly scraped the coating on the copper trace's of the circuit board, so I could solder two leads to them (this was NOT easy) then I attached my leads to the switch. I have a clip of me using the circuit on... I also modified the circuit by running it through a small amplifier to enhance the sound.

Goodhart made it!(author)2009-09-03

Very nice ! And so you did an Instructable on that? You can link to it from here, I don't mind. :-)

aeromancy made it!(author)2008-10-01

I have finally obtained some free time to go to radioshack. It turns out that they changed this once again, and the newer one sounds somewhat decent. This would still make a great Instructable for those people who have put the older one in the back of a closet, and just discovered how terrible the sound quality is, and how they can barely hear it again. This Instructable has also inspired me to make future projects.
Sorry if this disappointed you. :-(

Goodhart made it!(author)2008-10-01

No, it doesn't disappoint me, especially the phrase This Instructable has also inspired me to make future projects. That is my goal, if you can't do the actual project, inspiration is great too, but even if you COULD do the actual project, I like to inspire more from others. :-)

sounds like they may have gone back to the one they had before the recent dumb one that didn't work well. The one before the one I used in the project, cost a little more, but was way better. I have one of those too....

Goodhart made it!(author)2008-07-27

PS: I added one more comment to the last step this morning, giving a little more detail on my method of soldering in an extra LED in case someone wanted to do that.

Goodhart made it!(author)2008-07-22

Thanks, I still have to finish the "dressing it up" that I want to do as the last step, but otherwise it is pretty much finished. It is funny, 30 years ago, when things were not so small and compact, I bought the "CHIP" they sold then (I can't find it there now) and MADE my own digital recorder. That was one of my coolest projects as a youth. It was non-volatile for about 3 months or more even without power. A few years later, when I went back to buy it again, they no longer had them, but replaced it with a bigger "already made" board. It was $20 (the chip had been $35 or something like that). I bought one, and then forgot about it (I just found it very recently). Then when I wanted to do the April Fools contest, I needed one and bought the latest one, which as you found out, is not very loud, and if you shout into it, it gets all distorted sounding. It is junk. You are certainly welcome to try to make it work and if you have troubles, there are a few other things that can be done to eliminate distortion, clipping, etc that I can link to. OR, you could use an amp that doesn't quite have a 200x amplification :-) I could have used the speaker and tower as is and just plugged the output of the amp in to the speaker tower's input, but then I would need to plug the speaker into the wall and I didn't want to hamper it THAT much; it is bad enough that it is so big :-)

aeromancy made it!(author)2008-07-22

Isn't it amazing how technology advances? I look forward to when you add the last step/s. B y the way, this was an excellent Instructable.

Goodhart made it!(author)2008-07-22

Thank you. I tried to make it "evolve" as I corrected things along the way, but it got so it took sooo long to finish I had to publish beforehand or it might have been a few weeks more until I did. I am glad it was useful.

klueless made it!(author)2008-10-08

Way cool project. And what a great instructable, Goodhart. I especially appreciated the way you included us in your design process. I love that. I have designed a firing panel to ignite 8 flash pots for use in our Halloween haunted yard display. I thought how cool it would be to have the sound of thunder roaring after the flash from the flash pot. I looked around for a circuit that would do that and found a project built around an ISD1110 chip which gives about 12 seconds of record time and costs about $13 + S&H; from eBay.. It's too late to build that for this Halloween, but it was definitely on my list for next year's projects. Then this morning I was thinking bout this project and I wondered if I would be able to modify one of those inexpensive memo recorders. I only recently discovered, so I'm still not used to it being such a bountiful resource. But, I did search here and found your project. It is exactly what I was thinking about, and your detailed explanation of the process really helped me understand things so I can customize it when I do build it. Now I just need to find an instructable that will tell me how to trigger playback from a flash of light. Motion sensor or clap-clap trigger would be fun to. Thanks for taking the time to share this project and doing such a great job with it.

Goodhart made it!(author)2008-10-08

Thank you, I am glad my instructable became useful in some small way. PS: if you have a bit of an electronics background (hobbyist) you could find one of those sound activated toys (anything from some Elmo's to haunted house devices) and hack the sound activated switch. Just a quick thought.

Goodhart made it!(author)2008-07-27

Listen to the WAV to hear the quality of this improved device (if you have the original device, you will know right away the difference).

Goodhart made it!(author)2008-08-04

Does ANYONE think I need to fix, or make clearer anything here? I am wondering if I have left it TOO crude?

GorillazMiko made it!(author)2008-07-01

Amazing photos! Keep up the great work. +5/5 stars. (How's the shirt?)

Goodhart made it!(author)2008-07-01

Thanks; that last pic ( LM386 ) is not one I took though. It is a catalog picture blown up a bit.
I love the shirt. It will remind me of you all if I ever end up with dementia *sigh*

GorillazMiko made it!(author)2008-07-01

My brother's band's new song is called Dementia. Well, 2nd newest song. :P

Goodhart made it!(author)2008-07-17

PS: I have worn the white shirt twice now already, and the Robot one three times in public. I was even complimented on the Robot shirt at a Cardio-therapy session, so I explained what it was all about. :-)

GorillazMiko made it!(author)2008-07-17


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Bio: I am, most definitely older than 00010101 and to put it simply, still curious about nearly everything :-) I then tend to read and/or experiment ... More »
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