555 IC Tester

[Yorkie]

I mentioned in another thread that I’ve got rather a lot of 555 ICs of doubtful provenance, and as I've recently been making a few gadgets which use this versatile little IC, I thought it would be useful to make a simple tester to see if I have any duds. Circuits for such testers - often built on strip-board - abound on internet and I claim no originally for the circuit that I used. I’m not a great fan of strip-board so I designed a little PCB on which to build the tester.

The circuit is basically an astable multivibrator, and when the test button is pressed, if the IC under test is good, the two LEDs will flash alternately.

With the component values chosen, the flash rate is about 3 Hz for each LED. (The frequency of flashing is of no importance, and is determined by the values of R1, R2 and C1). The way that it works is that when the test button is pressed, C1 starts to charge through R1 & R2, and when the voltage rises to two-thirds of the supply voltage the flip-flop internal to the IC will toggle, then pin 7 goes low and C1 starts to discharge. When the voltage across C1 falls to one third the supply voltage, the flip-flop resets and pin 7 goes high, then C1 starts to charge up again and the cycle is repeated. If the IC is good, the two LEDs will continue to flash alternately as long as the test button is pressed.

All the bits were from my spares box - another little 'MFJ' project - 'made from junk'! As is my custom, I made a little comb-jointed oak box in which to house it. The question arose as to how to devise a test socket for the IC. I just soldered a turned-pin socket into the PCB, then added another five pushed into each other, with the uppermost one glued to the front panel with epoxy glue, and the PCB mounted on stand off pillars below the front panel.

Hardly breaking new ground here, but I thought I’d share it should anyone else ever wish to make a 555 tester.

Pics of the the circuit, PCB artwork, component overlay and finished tester are attached. The PCB 6.5 x 5.5 cms.

The 555 is a remarkable little IC, introduced in 1971 by the US firm Signetics, and still in widespread use for such things as timers and oscillators. It’s now made by many companies in the original bipolar form and also in low-power CMOS types ‘7555’. By 2003 it was estimated that 1 billion were made every year.

http://en.wikipedia.org/wiki/555_timer_IC

In terms of longevity, it must rank alongside the 741 op-amp, introduced in 1968, and 2N3055 transistor, which had its 50th birthday in 2014!

Hope that’s of interest to someone. 

[tiv48]

I love it. So simple yet elegant.
Rob T

[ex 2 Base]

Hello David you have been at it again making those smart boxes, well done. I use a little board bought from RS for use with 555 timers, for my PWM motor controllers they used to be about 50p each bought in a pack of 5. I remember how expensive they used to be and 741. I had a 741 in daily use for more than 28 years, we made ourselves a Solar hot water system and a 741 controlled the system, never failed. Then we sold the lot and now have PV panels on the roof .Ted

[Yorkie]

Thanks for reading the thread Rob & Ted, and for your  kind comments.

I recall you mentioning before Ted about your  'home-brew' solar hot water system - didn't know you'd gone all 'posh'  with PV panels!

(Surprised you haven't got a wind turbine, being on the N.E. Coast with bracing winds).

[Mark Hennessy]

Very nice! And now we know why you were talking about 8 pin IC sockets the other day

In the past I've used wire-wrap sockets to get the "elevation", but I imagine these are pretty much extinct these days?

You honestly can't beat the look of a nice wooden box. So much more tactile than a metal box. As I say, very nice...

[thomass]

Hello David,

Very nice,  I love your wooden boxes you create to house your projects.   I've been inspired to build my own 555 IC tester using an RS 434-071 ready made PCB for assembling and evaluating DIP8 555 timer circuits.    

Thomas

[Radio Fixer]

Could do the electronics but not the boxes. They are almost too good, must be able to make them very easily now David. Do you set up and make a stack?

Gary

[Yorkie]

No Gary - I usually make the project, then make a box to suit. I try to use offcuts of mahogany which I scrounge from here and there, but failing that, I use oak, which I'm not very fond of. Really, the most time consuming part of slicing the wood on the band-saw to about 7mm thick, then sanding it smooth on a belt-sander. Then having cut the wood to size, I use a home-made router jig to cut the comb joints. I usually use scrap SRBP PCB sheet for the front panel, sprayed white, or sometimes I design a simple front panel on coloured paper and laminate it, then make an acrylic panel to go on top from 2mm acetate glazing sheet.

To be honest, though I get lots of encouraging comments about the little boxes, it only calls for basic woodworking skills, a cheap DIY store router and time, which I often don't have. Of course, it's only viable if people see it as an interest rather than a chore. Woodworking isn't everyone's cup of tea.

There's no logic to it of course - it can take almost as long to make the box than to make a simple project that goes in it, but it enables me to indulge in both woodworking, and electronics, as time permits. The most recent box I made was for a chum who's new to the hobby and had built a Velleman K700 signal tracer/injector kit. He'd built the PCB, didn't have a speaker, sockets, switch etc and had lost his way a bit,  so I boxed it up for him.

I started making the boxes because it's not always easy to find ABS project boxes of just the right size, (and they're not often cheap either), apart from which I think the wooden jobbies have more of a 'vintage look' about them, evocative of the crystal sets of yesteryear, so are a bit more in keeping with the hobby. And of course, there's the added frisson from 'mekking summat from now't', which has great appeal in this neck of the woods, especially to the likes of me, born at the onset of the 'make do and mend' era .