Late last year Silicon Chip published the circuit for one. Unusually for them, it didn't work exactly as expected so they put in a heap of effort, producing circuit diagams for several units - some with UHF telemetry. Pump control was part of it. You had a number of options - display via bar graph, etc. Google "Silicon Chip magazine" and you will be able to backorder the issues.
Email the tech dept first, it spans more than one issue. They will tell you what you need to order. Their final product, or family of products is microprocessor based (downloadable code from their site, and also in-circuit programming).
In the US you buy the chip from Anderson Electronics (email me for their address if you decide to go ahead - the chip isn't widely admired in the US - it is English designed and built and thashes many US products - and at a fraction of the price). In one comparison a US magazine did, it ran their test micrprocessor against a PICAXE, and it just beat it. Problem was, the PICAXE was running at 4Mhz and their was running at 20Mhz. When the PICAXE was set to 16Mhz, the results were, well ... a lot better and not published (except for a paragraph saying the PICAXE hadn't performed as badly as reviewed).
After Silicon Chips embarrassment of featuring something that didn't work very well, they more than made up for it by producing a device with several options (like how the pump controls work, UHF transceiver operation, etc).
If you haven't seen Silicon Chip magazine and do decide to order it (about $US7.50 per issue), you will be in for a surprise, it is a high quality magazine with very good articles, and not aimed at people who have PHds in electrial engineering. Construction details are precise (painfully so sometimes), the PCB is orderable as well as a silkscreened box. Their circuit diagrams are a joy to follow and well above average in quality. Full online support and detail of where to buy everything. Their email is firstname.lastname@example.org - I haven't checked but you may find more detail on this unit on their site as well.