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Earphone radio 1968 009

nobody@ipernity.com (GrahamH) — Mon, 07 Jan 2013 08:29:36 +0000

GrahamH has posted:

A pocket personal portable AM (no FM at that time) radio which I built in a 36 exp slide box at the start of the 68/69 Christmas school holidays. It was originally built breadboard style with a valve-style tuning capacitor. The circuit has three transistors. The signal path flows from the ferrite rod to the first transistor for RF amplification with regeneration. A diode demodulates the signal which is sent back to the first transistor reflexed as the first AF stage. Two more transistors cascaded give more AF gain. A high impedance crystal earpiece couples the audio to the Listener. Performance was adequate for primary coverage areas. See Notes on 005.

Earphone radio 1968 007

nobody@ipernity.com (GrahamH) — Mon, 07 Jan 2013 08:27:38 +0000

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Earphone radio 1968 008

nobody@ipernity.com (GrahamH) — Mon, 07 Jan 2013 08:28:38 +0000

GrahamH has posted:

Earphone radio 1968

nobody@ipernity.com (GrahamH) — Mon, 07 Jan 2013 08:30:49 +0000

GrahamH has posted:

A pocket personal portable AM (no FM at that time) radio which I built in a 36 exp Kodak slide box at the start of the 68/69 Christmas school holidays. It was originally built breadboard style with a valve-style tuning capacitor. The circuit has three transistors. The signal path flows from the ferrite rod to the first transistor for RF amplification with regeneration. A diode demodulates the signal which is sent back to the first transistor reflexed as the first AF stage. Two more transistors cascaded give more AF gain. A high impedance crystal earpiece couples the audio to the Listener. Performance was adequate for primary coverage areas. See Notes on 005.

An oldie added to kick off the Macgyverering group. Using a 36 exp Kodak slide box as a radio case.

Earphone radio 1968 006

nobody@ipernity.com (GrahamH) — Mon, 07 Jan 2013 08:26:22 +0000

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Earphone radio 1968 005

nobody@ipernity.com (GrahamH) — Mon, 07 Jan 2013 08:25:06 +0000

GrahamH has posted:

A pocket personal portable AM (no FM at that time) radio which I built in a Kodak 36 exp slide box at the start of the 68/69 Christmas school holidays. It was originally built breadboard style with a valve-style tuning capacitor. The circuit has three transistors. The signal path flows from the ferrite rod to the first transistor for RF amplification with regeneration. A diode demodulates the signal which is sent back to the first transistor reflexed as the first AF stage. Two more transistors cascaded give more AF gain. A high impedance crystal earpiece couples the audio to the Listener. Performance was good for primary coverage areas.

Earphone radio 1968 003

nobody@ipernity.com (GrahamH) — Mon, 07 Jan 2013 08:23:46 +0000

GrahamH has posted:

Resistor's new home

nobody@ipernity.com (.:madworm:.) — Tue, 20 Nov 2012 09:44:41 +0000

.:madworm:. has posted:

Offender removed

nobody@ipernity.com (.:madworm:.) — Tue, 20 Nov 2012 09:44:42 +0000

.:madworm:. has posted:

Hopefully fixed - 8 more to go

nobody@ipernity.com (.:madworm:.) — Tue, 20 Nov 2012 09:44:43 +0000

.:madworm:. has posted:

So far I've managed to kill 5 of these PT4115 LED drivers, and I don't think that I've abused them - at least when compared to what I've done to other devices that survived no problem.

The failure mode is very consistent. Either it stops working altogether (no more switching, output switch permanently open) or the output switch is permanently closed and the LEDs suffer over-current.

Common to both manifestations is that the DIM pin shows unusually low resistance (about 6Ω) to GND. This makes me believe that this pin gets trashed somehow. Therefore I will test if adding a Zener + dropper resistor will help to protect the chip. Voltage clamping at 5V1 definitely works, so lets see how things go.

Adding a Zener + resistor is the way to go. No more premature demise.

Tinned

nobody@ipernity.com (.:madworm:.) — Tue, 20 Nov 2012 09:44:40 +0000

.:madworm:. has posted:

Mask removed

nobody@ipernity.com (.:madworm:.) — Tue, 20 Nov 2012 09:44:39 +0000

.:madworm:. has posted:

Waiting resistor

nobody@ipernity.com (.:madworm:.) — Tue, 20 Nov 2012 09:44:39 +0000

.:madworm:. has posted:

About to cut a trace

nobody@ipernity.com (.:madworm:.) — Tue, 20 Nov 2012 09:44:37 +0000

.:madworm:. has posted:

Cut trace

nobody@ipernity.com (.:madworm:.) — Tue, 20 Nov 2012 09:44:38 +0000

.:madworm:. has posted:

The result is pretty good. I think I could use an even smaller tool (spear-point drill). Using sub-1mm fluted end-mills can get a bit tricky, especially if they're not of the short and stubby kind. They break quite easily - and cost a lot.

Planned ESD protection

nobody@ipernity.com (.:madworm:.) — Tue, 20 Nov 2012 09:44:37 +0000

.:madworm:. has posted:

1k dropper resistor + 5V1 Zener diode BZX84C5V1.

PT4115 driver - modded

nobody@ipernity.com (.:madworm:.) — Mon, 02 Jan 2012 19:25:02 +0000

.:madworm:. has posted:

I've added a signal wire going to the 'dim' pin and wires getting the rectified voltage.

Diode bugfix

nobody@ipernity.com (.:madworm:.) — Thu, 21 Jun 2012 09:16:32 +0000

.:madworm:. has posted:

Not ideal (free-standing TO-220), but tolerable for a bug-fix. The diode's characteristics are quite good.

Datasheet

Diode bugfix

nobody@ipernity.com (.:madworm:.) — Thu, 21 Jun 2012 09:16:32 +0000

.:madworm:. has posted:

Not ideal (free-standing TO-220), but tolerable for a bug-fix. The diode's characteristics are quite good.

LEDs

nobody@ipernity.com ({ME}) — Wed, 28 Nov 2007 16:23:33 +0000

{ME} has posted: