$10 Monitor for Minstrel or Mini PET kits

How about a mini monitor for a Mini PET?

I am occasionally asked about HDMI converters for things like the Minstrel and Mini PET kits. I have not tried many of those, but in general they don't like monochrome composite video. The lack of the colour burst signal confuses them, and so they don't detect it, or try to see colour where there is no colour.

George Beckett has a Dell monitor which does similar things:

Normally most older LCD monitors are quite happy with those signals, and it is sometimes cheaper to buy a monitor with a composite input than an HDMI converter for an existing one.

Case in point, a $10 LCD designed to be used as a car reversing / DVD player monitor. I had used several different versions of this type of thing, so I thought I would try the smallest and cheapest and see if it was still viable.

There seem to be many of these around with different brands and part numbers, but the same things inside.

These usually run from 12V, although in some places they say 12-24V, and in practice, they run fine from 9V.

They usually have three plugs, one 2.1mm DC jack (centre positive) and two phono jacks.

Contrary to the photo on the listing, the red one is the power jack.

You can use either input, and if you have two devices connected, the one in the white jack takes priority. I think the idea is you connect a DVD player to yellow and the reversing camera to white, so that when reverse is engaged, the reversing camera is shown, then when you go back to drive, it switches back to your movie. If that isn't already illegal, then it really should be.

I would recommend using the yellow jack, particularly with something like the Minstrels, as it switches between white and yellow when the sync drops, as it does on the Minstrel 2 when you press a key, and on the Minstrel 3 when you enter a line of code.

The screen is very bright, not sure the brightness control does anything, this was brightness 0, and still washed out the whole screen so you couldn't see it.

You can just about make it out in this photo.

However, looking at the screen itself, it is quite readable.

I did better taking a picture with a "white on black" screen on the Mini PET.

The specification (if you can believe it), shows the resolution of this 4.3" LCD as 480x272.

That should be good enough to read the 32 or 40 character displays (32x8 = 256 pixels, 40x8 = 320 pixels).

It is certainly good enough to see what is going on.

Where there is the option, setting to NTSC works better as that reduces the borders and more closely matches the lines available.

However PAL also works.

The display updates are also fast enough to use the machines as normal.

Of course I am going to have a go at Tut-Tut.

Those sort of displays are available in 3.5, 4,3, 5.0 and 7.0 inch formats, from as little as $10, so a useful thing to have around.

The one shown here cost me £9.99 delivered from Amazon.

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Minstrels and Mini PETs

Minstrel and Mini PET kits and ready built units are available from my Tindie store.

https://www.tindie.com/stores/tynemouth/

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IKA Logic SQ200 Logic Analyser Review

This is a new toy I have just got, I've only had it a few days, but I've been quite impressed so far. It is an SQ200 from IKA logic, a 200MHz 4 channel logic analyser / signal generator.

I've been using a DSLogic Pro for the last three or four years, until last month it stopped being detected properly. It is one of those things which has the firmware loaded onto it by the driver, so it connects as one type of device, get the firmware, disconnects and then reconnects as the proper device. That has stopped happening now, and I've not been able to get it to identify properly, so it's bricked, currently waiting to hear back from support to see if there is anything they can do.

In the interim, I have been using a cheaper generic clone of something or other from ebay. It works, but has a sample rate of 24Mhz, which means it's not accurate enough to things changing at 16Mhz. I am currently working on the firmware for the Mini PET video controller, and the timing has to be precise down to one instruction of it's 16Mhz clock, and that is down in the sample noise of that unit.

So, time to get something that's a lot faster. This is 200Mhz, so is rather to be able to cope with signals up to 50Mhz, which is more than enough for what I need at the moment. It's limited to four channels, which is not ideal for some of the other things I do where 16 or more would be useful. But for serial protocols like UART, I2C, SPI etc. and the current video signalling it's great.

The unit comes with a USB lead and some probes. It's a very small box, 50mm square, but I guess it doesn't need to be any larger.

I wasn't too impressed with the quality of the supplied probes, those sort of clips aren't very good with IC legs. The connector at the device end is just a 5 way 0.1" connector, which is great, so you can make up your own leads. Not sure how that will work out with the higher frequency signals, but I guess just keep the leads short.

I have made up a set using the EZ Hook clips I have been using, these were a bit expensive, but have been worth it.

Because it is a easy connector to use, I have also made up a custom lead for the current job so I don’t need to clip multiple probes on each time.

The software is custom, and it is not currently supported by the open source sigrok Pulseview programs I have been using. So far it seems very nice and is doing what I need.

At 200Mhz I can capture 20mS, which is enough for a frame of video, and I can zoom down to line and pixel detail.

The issue I am currently dealing with is based on timing of the HSync pulses. They should all be 24uS high followed by 40uS low, but somewhere there is one that is slightly out. The dot clock on the PET video is 8MHz, so each pixel is 125nS wide. 

One instruction cycle on the microcontoller is 62.5nS, so a couple of instructions out and you are one pixel to the right of where you should be. Most of the code is NOP instructions so there are only a couple of NOPs to move around to fix it.

Various tweaks to the timing have given me close to the correct result, but each of the video modes needs to be dialled in to the exact timing. Ah, there's one of the culprits that 40us pulse is 60nS longer that it should be. One NOP instruction removed and it's now 40.000uS.

That is enough to change the video output from...

...to

A nice straight line, and with all the other timing tweaks, composite and drive to CRT monitors is now all working nicely with nice straight edges on the side.

The SQ200 has a lot of functionality I have yet to investigate fully. One thing that looks very handy is being able to set a conditional trigger, only trigger when that signal is low and that one goes high, then low before the other one goes high, and things like that.

It had protocol decoders built in, so you can decode I2C etc.

It can work as a signal generator, and can also work as mixed input and output, so it can actually send I2C commands and display the results.

So that's looking like a very handy tool to have, and helped me finish off the last few tweaks to the PET video firmware.

Atmel AVR Programming Clip Review

This is an old post, preserved for reference.

The products and services mentioned within are no longer available.

I've bought one of these recently, and it's great.

What is it? It is a clip to make temporary connections to a board with a microcontroller on to program it.

There is a standard pinout for programming Atmel AVR chips, a 6 pin 2x3 pin header with the following pinout. You'll see this on all sort of boards, there's even two of them on an Arduino board.

There are various programmers, from the very simple to the full features ones from Atmel themselves. The one I mostly use is the USBtiny ISP from Adafrruit.

This has an IDC connector on the end of the cable. On the early boards, and ones in active development, I solder a pin header onto the board.

For production boards, I tend to leave the holes in the board.

To program these, I insert the pin headers into the cable.

These will make a good enough connection, if held at an angle for the 10-20 seconds that it takes to program the chip.

And that's how I've been using it for years. I must have gone through half a dozen cables, as the ribbon starts to fray at the edge of the connector.

I have looked around for something to do this better, but most of the things I found need to be added as part of a programming jig. I was looking for something quick and simple. I then saw someone on Tindie selling a 6x1 programming clip.

That looked almost ideal, and I was going to get one as I do have a few boards which use the 6x1 layout with pads on the back, for a production programming jig.

I asked the seller DSTIKE, if they had a 3x2 option, and it they said one was planned, so I ordered one of each.

They arrived very nicely packed, and well protected.

This was just what I was looking for. The clip opens up, you slide it over the edge of the board and it locks in place with the 6 pins in the holes on the PCB.

You can then program the chip without having to hold it in place.

The IDC cable from the programmer plugs into the top.

And there is a clamp at the end so you can hold the wire in place (to stop it flexing and fraying like it used to do).

That's been working really well, so it is now a permanent fixture on my programmer.

The cynical amongst you (i.e. the first person I told about this), could say you could knock something up from a clothes peg. Well, maybe, but this opens wider, has all the connections already in place etc., and wasn't that expensive, so I'm very happy with it.

So, all in all, full marks, if you are interested in something like this, here is the link again to DSTIKE's Tindie store.

Update:

Disaster. The plastic on the bottom of the clip has shattered.

Now fixed thanks to a wooden chip fork.

2022 Update: I have still use these, but have removed the lower section all together and just hold it in place.